Worcester 28Si User guide

25Si / 28Si
WALL MOUNTED COMBINATION BOILERS FOR CENTRAL HEATING
AND MAINS FED DOMESTIC HOT WATER
INSTALLATION AND
SERVICING INSTRUCTIONS
This appliance is for se with Nat ral Gas or LPG (Cat II 2H3P).
25Si GC NUMBER 47 311 49 (N.G.) CG NUMBER 47 311 50 (L.P.G.)
28Si GC NUMBER 47 311 51 (N.G.) CG NUMBER 47 311 52 (L.P.G.)
APPLIANCE OUTPUTS
Domestic Central Heating
Hot Water
25 28 25 28
Minimum 8.5 kW 8.5kw 8.5 kW 8.5kw
Maximum 25.0kW 28.0kw 25.0kW 28.0kw
IMPOR AN : HESE INS RUC IONS APPLY IN HE UK ONLY
AND MUS BE LEF WI H HE USER OR A HE GAS ME ER
Read the instructions before starting work - they have been written to make
the installation easier and prevent hold-ups.
0I

1.1 Gas Safety (Installation & Use) Regulations 1998.
It is the law that all gas appliances are installed by a competent
person in accordance with the above regulations. Failure to
install appliances correctly could lead to prosecution. It is in
your interest, and that of safety, to ensure compliance with the
law.
1.2 he manufacturers notes must not be taken, in any way, as
overriding statutory obligations.
1.3 he compliance with a British Standard or European Norm
does not, in itself, confer immunity from legal obligations.
1.4 he installation of the appliance must be in accordance with
the relevant requirements of the Gas Safety Regulations, current
IEE Regulations, Building Regulations, Building Standards
(Scotland) and local water bye-laws.
1.5 he installation should follow the recommendations of the
following British Standards unless otherwise indicated and to
any other relevant standards.
BS5440:1 - Flues and ventilation for gas appliances: Flues
BS5440:2 - Flues and ventilation for gas appliances: Air supply.
BS5449 - Central heating for domestic premises.
BS5482 - Domestic propane gas burning installations.
BS5546:1 - Installation of gas hot water supplies.
BS6700 - Domestic water supply (when relevant).
BS6798 - Installation of gas fired hot water boilers.
BS6891 - Low pressure gas pipework installations up to 28mm
(R1).
BS7593 - Water treatment.
1.6 he appliance and/or components must conform, where
applicable, to all relevant Directives.
1.7 In accordance with COSSH the appliance does not contain
any substances which are harmful to health.
1.8 Product Liability regulations indicate that, in certain
circumstances, the installer can be held responsible, not only for
mistakes on his part but also for damage resulting from the use
of faulty materials. We advise that to avoid any risk, only
quality approved branded fittings are used.
1.9 LPG Installation. he appliance shall not be installed in a
room or internal space below ground level when it is intended for
use with LPG. his does not preclude the installation into rooms
which are basements with respect to one side of the building but
open to the ground on the opposite side.
1.10 hese instructions cover, as far as possible, the foreseeable
situations which may arise. Contact Worcester Heat Systems
echnical Department, elephone: 0990 266241, for advice on
specific installations.
he Benchmark initiative is the new code of practice to
encourage the correct installation, commissioning and servicing
of domestic central heating boilers and system equipment.
The 'Log-book' is a vital doc ment that m st be completed
by the installer at the time of installation. It confirms that the
boiler has been installed and commissioned according to the
man fact rers instr ctions.
Without the completion of the Log-book, manufacturers may refuse
to respond to a call-out from a householder, who will be advised
that he or she must call back the installer, who has not fulfilled his
obligations to record the information required by the initiative.
It is important that:
he services and the system are properly flushed as specified.
he User is clearly instructed on the correct operation of the appliance.
he benefits of regular servicing are explained - to maintain the
efficiency and extend the life of the appliance.
2.1 General Information
he appliance is set to give the maximum output of 28 kW [28Si]
or 25kW [25Si] to the domestic hot water and to the heating
system. he hot water flow rate is limited to a nominal 10 l/min
[28Si] or 9 l/min [25Si] at a maximum temperature rise of 40°C.
he sanitary water section of the appliance is suitable for mains
water pressure of upto 10bar.
Kits are available to convert the appliance from Natural Gas to
Propane operation and vice versa.
2.2 Electrical Supply
230V - 50Hz. Load 180 watts. External fuse 3A, Internal fuses F1
- 2A, F2 - 1.6A (20mm).
2.3 Gas Supply
he appliances require a maximum of 3.38 m3/h of natural gas
(G20) or 1.25 m3/h of propane (G31) [28Si] or 2.98 m3/h of
natural gas (G20) or 1.12 m3/h of propane (G31) [25Si].
he installation and the connection of the gas supply to the
appliance must be in accordance with BS6891.
he meter or regulator should deliver a dynamic pressure of 20 mbar
(G20) or 37mbar (G31) at the appliance, which is equivalent to about
18.5 mbar or 36 mbar at the gas valve inlet pressure test point.
2.4 Installation
he appliance is suitable for indoor installation only and for use
with a sealed system only.
Do not place anything on top of the appliance.
It is a room sealed appliance and a separate combustion air
supply is not required in any room or compartment in which the
appliance is fitted.
If the appliance is fitted in a cupboard or a compartment is built
around it after installation, then the structure must conform to
the requirements of BS6798 and BS5440 Part 2. However,
because of the low casing losses, there is not a need for the
cooling ventilation openings in the compartment. The spaces
specified in Section 6. Air S pply m st be provided.
here is space for the service pipes to pass at the back of the appliance.
2.5 Flue
he flue can be to the right, left or rear. A vertical flue system is available.
he flue terminal, on the outside wall, must not be obstructed or damaged.
An internal flue fitting kit is available. Fitting instructions are
given in Section 11.9.
2. Introduction1. Installation Regulations
2
1. Installation Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 9. Gas Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2 10. Electrical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9
3. echnical Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 11. Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 12
4. Siting the Appliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6 12. Commissioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 18
5. Flue erminal Positions . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 13. Handover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 20
6. Air Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 14. Inspection and Servicing . . . . . . . . . . . . . . . . . . . . . . . . . Page 20
7. Sealed System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 15. Replacement of Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 22
Open Vent System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 16. Short Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 28
8. Domestic Hot Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9 17. Operational Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . Page 30
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18. Fault Finding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 32
Contents

2.6 Controls
Controls for switching the appliance On or Off and for adjusting
the CH and DHW temperatures. he CH control knob also
switches the CH off and on.
A programmable room thermostat or a facia mounted
programmer or clock is available.
A room thermostat and/or an externally mounted programmer
for mains voltage operation may be connected to the appliance.
Only do ble ins lated mains voltage controls not req iring
an earth can be sed.
2.7 System
All dirt must be flushed from the system before
connecting the appliance.
he system can be pre-piped and flushed before the appliance is fitted.
he connections in the system must withstand a pressure of
upto 3 bar.
Radiator valves must conform to BS2767: 10:1977.
able 3 gives the pump head available for the system and the
required temperature differential.
A drain cock must be fitted to the lowest point and an air vent to
the highest point of the system.
2.8 Showers, Bidets, aps and Mixing Valves
All taps and mixing valves must be suitable for the available
mains pressure and temperatures up to 65°C. It may be
necessary to fit a pressure reducing valve.
Hot and cold mains fed water can be supplied to overrim bidets
but is subject to local water company requirements.
he flow of water from individual outlets varies on all mains fed
systems that are not fitted with flow balancing valves. If a
pressure equalising valve is fitted then the domestic hot water
temperature should be set to maximum.
hermostatically controlled shower valves give extra comfort
and protection.
2.9 Safety
he appliance must not be operated with the inner casing cover removed.
he gas and electricity supplies must be turned off before
working on the appliance.
emperature monitoring controls are fitted to prevent overheating.
Automatic frost protection is provided together with automatic
pump seizure protection.
he gas valve solenoids are automatically checked for gas soundness.
IMPORTANT: Where back-flow prevention devices, incl ding
water meters, are fitted the expansion of hot water into cold
water main can be prevented. This can res lt in a press re
b ild- p that may ca se damage to the boiler and ho sehold
devices s ch as showers, washing machines etc.
In these cases we recommend that a mini-expansion vessel be
fitted adjacent to the boiler in the cold water pipe.
2.10 Operation
Central Heating
A demand for heat will ignite the burner. It will operate at
minimum pressure for 2 minutes before increasing to the maximum
pressure over a period of 1 minute and then automatically
match the system requirements. At the end of the demand the
burner will go out, the pump will continue to run for up to 4
minutes or the fan for 35 seconds. here is an anti-cycle time of 3
minutes.
Domestic Hot Water
A demand for hot water will ignite the burner. he burner
pressure will immediately rise to maximum.
At the end of the demand the fan will continue to run for 35
seconds if there is no heating demand.
he demand for hot water will override the CH function. In winter
it may be necessary to reduce the flow at the taps to maintain
the delivery temperature.
2.11 Conversion Instr ctions
he appliance can be converted from LPG to NG and vice versa
by replacing the burner and resetting the gas valve.
o replace the burner and transfer the electrodes refer to Section
15.4.2,3 and 4. he burner part numbers are:
NG (25Si and 28Si) 8 718 120 565 0
LPG (28Si) 8 718 120 566 0
LPG (25Si) 8 718 120 569 0
o reset the gas valve refer to Section 15.4.4, Section 12-
Commissioning and , for setting pressures, able 1 in Section 3-
echnical Data.
Always check for gas soundness after replacing components in
the gas circuit.
3
Fig. 2. Water flow diagram.
0I
Fig. 1. Facia controls
Mains
ON/OFF
Switch
Power ON
Indicator
Central Heating
Operation and
emperature
Control Knob
Domestic
Hot Water
emperature Control
Knob
Central Heating
Indicator
Light
Domestic Hot
Water Indicator
Light
Burner
Operation Light
System
Pressure
Gauge
Reset
Button
!
1 2 3 4 5
7
8
6
9
10
11
12
1. CH Flow.
2. Domestic Hot Water
Supply.
3. Domestic Cold Supply.
4. CH Return.
5. Relief Valve Discharge.
6. Relief Valve.
7. Domestic Water Flow
Switch.
8. Pump.
9. Sealed System
Expansion Vessel.
10. Bi-thermal Gas to Water
Heat Exchanger.
11. Automatic Air Vent.
12. Fixed By-Pass.

he data plate is fixed to the inner casing cover.
4
3. Technical Data
MAXIMUM AVAILABLE PUMP HEAD
BOILER OU PU HEAD MIN. FLOW RA E
kW Metres L/min. °C
8.5 5.9 11.0 11
25 2.0 30.5 12
28 2.0 30.5 13
Table 3
FLUE DETAILS
HORIZONTAL FLUE mm
WALL HOLE DIAME ER EX ERNAL FIX 110
IN ERNAL FIX 150
S ANDARD FLUE MINIMUM LENG H 330/425 *
MAXIMUM LENG H 725
EX ENDED FLUE MAXIMUM LENG H 2975
FLUE ASSEMBLY DIAME ER 100
Table 2.
FLOW/RE URN
DIFFEREN IAL
* NOTE : Fl e lengths between 330 and 425mm req ire the fl e to be c t
MECHANICAL SPECIFICATIONS
CEN RAL HEA ING FLOW - COMPRESSION 22mm
RE URN - COMPRESSION 22mm
COLD WA ER INLE - COMPRESSION 15mm
DOMES IC WA ER FLOW - COMPRESSION 15mm
GAS INLE Rp 3⁄4
RELIEF VALVE DISCHARGE (PUSH FI ) 15mm
CASING HEIGH 800mm
CASING WID H 440mm
CASING DEP H 360mm
WEIGH - LIF 42.3kg
WEIGH - UNPACKED 45.8kg
WEIGH - PACKAGED 52kg
Table 4
NOMINAL BOILER RATINGS (10 Min tes After Lighting)
BOILER ADJUSTED FOR G20 (Nat ral Gas)
OU PU INPU (Net) GAS RA E
kW kW m bar. m3/h
8.5 10.5 0.7 1.12
28.0 31.1 14.1 3.38
BOILER ADJUSTED FOR G31 (Propane)
8.5 10.5 2.3 0.42
28.0 31.1 35.5 1.25
Table 1. 28Si
BURNER
PRESSURE
NOMINAL BOILER RATINGS (10 Min tes After Lighting)
BOILER ADJUSTED FOR G20 (Nat ral Gas)
OU PU INPU (Net) GAS RA E
kW kW m bar. m3/h
8.5 10.5 0.7 1.12
25.0 27.8 11.5 2.98
BOILER ADJUSTED FOR G31 (Propane)
8.5 10.5 4.2 0.42
25.0 27.8 35.7 1.12
Table 1. 25Si
BURNER
PRESSURE
Natural Gas: Net Input = Gross Input x 0.901 LPG (Propane): Net Input = Gross Input x 0.922

5
GAS SUPPLY SYSTEM - BASED ON NG (G20)
TOTAL LENGTH OF GAS SUPPLY PIPE (COPPER) metres
3 6 9 12
GAS DISCHARGE RA E - PRESSURE DROP 1mbar. m3/h PIPE DIAME ER mm
8.7 5.8 4.6 3.9 22
18.0 12.0 9.4 8.0 28
Table 7
CLEARANCES (mm)
INSTALLATION SERVICE
ABOVE APPLIANCE AND/OR FLUE ELBOW 30 30
IN FRON OF APPLIANCE 600 600
BENEA H APPLIANCE 200 200
RIGH AND LEF HAND SIDE 10 10
Table 8
SYSTEM CAPACITY
TOTAL SYSTEM VOLUME litres
INI IAL INI IAL CHARGE PRESSURE bar
PRESSURE bar 0.5 1.0 1.5
1.0 57 75 N/A
1.5 31 42 52
Table 9
PERFORMANCE SPECIFICATIONS 25Si 28Si
PRIMARY WA ER CAPACI Y litres 2.0 2.0
MAXIMUM MAINS INLE PRESSURE bar 10 10
MINIMUM MAINS INLE PRESSURE (WORKING) FOR MAXIMUM FLOW bar 1.1 1.3
MINIMUM MAINS INLE PRESSURE (WORKING) FOR OPERA ION bar 0.5 0.5
DOMES IC HO WA ER EMPERA URE RANGE °C 40 - 62 40 - 62
MAXIMUM CEN RAL HEA ING FLOW EMPERA URE °C 82 (nom) 82 (nom)
MAXIMUM CEN RAL HEA ING SYS EM SE PRESSURE bar 2.5 2.5
MINIMUM CEN RAL HEA ING SYS EM PRESSURE bar 1 1
OU PU O DOMES IC HO WA ER kw NA URAL GAS (G20) 8.5 - 25 8.5 - 28.0
LPG - PROPANE (G31) 8.5 - 25 8.5 - 28.0
OU PU O CEN RAL HEA ING kw NA URAL GAS (G20) 8.5 - 25 8.5 - 28.0
LPG - PROPANE (G31) 8.5 - 25 8.5 - 28.0
DOMES IC HO WA ER SPECIFIC RA E - 30°C RISE l/min 12.0 13.4
MAXIMUM DOMES IC HO WA ER FLOW RA E - 40°C RISE l/min 9.0 10.0
NOx CLASSIFICA ION FOR BO H 25 & 28Si Class 2
SEDBUK NUMBER 78.0 78.2
SEDBUK BAND D D
Table 5
Refer to Section 6.
DOMESTIC HOT WATER TEMPERATURE RISE
DISCHARGE RA E l/min 7 8 9 10
EMPERA URE RISE °C 25Si 51 45 40 36
EMPERA URE RISE °C 28Si 57 50 45 40
Table 6

he appliance may be installed in any room but refer to the
requirements of the current IEE Regulations and, in Scotland, the
relevant electrical provisions of the Building Regulations with
respect to the installation of appliances in rooms containing
baths or showers.
Where a room sealed appliance is installed in a room containing
a bath or shower, any switch or appliance control using mains
electricity must NO be able to be touched by a person using the
bath or shower.
he appliance is NO suitable for external installation.
No special wall protection is required.
he wall must be able to support the weight of the appliance.
Refer to able 4.
he specified clearances must be available for installation and
servicing. Refer to able 8, Fig.3, 4 and Section 6. Air Supply.
he appliance can be installed in a cupboard/compartment to
be used for airing clothes providing that the requirements of
BS6798 and BS5440 Part 2 are followed. Refer to Section 2.4.
he airing space must be separated from the boiler space by a
perforated non-combustible partition. Expanded metal or rigid
wire mesh is acceptable provided that the major dimension is
less than 13mm.
he clearance between the front of the appliance and the
cupboard/compartment door should be not less than 75mm.
LPG Installation. Refer to Section 1.9.
4. Siting The Appliance
Fig.4. Appliance casing dimensions and
req ired clearances (side view).
All dimensions in mm
Fig. 5. Side fl e opening
A CH Flow = 55
B DHW Flow = 120
C Gas = 185
D Cold Water Inlet = 250
E CH Return = 315
F Relief Valve Discharge = 375
Fig. 3. Appliance casing dimensions and
req ired clearances (front view).
All dimensions in mm
30
170
10
10
6
A
B
C
D
E
190
(A, B, C, D,)
20
A B C D E
View on underside of appliance showing
connections
Valves shown closed.
Fig. 6. Pipework connections
All dimensions in mm
440
106
600
800
230
200
360
200
230
200
F
All dimensions in mm
NOTE:
Casing is
3mm above
the top of the
wall mounting
frame. Refer to
Fig.15.
106
F

he flue system must be installed following the requirements of
BS5440: 1.
Standard flue kit length is 330 - 725mm (as measured from the
centre of the flue turret) with extension kits for flues up to
2975mm measured from the centre line of the flue turret.
he terminal must not cause an obstruction or the combustion
products a nuisance.
Under some conditions the terminal might steam and positions
where this might be a nuisance should be avoided. Refer to Fig 7
If the terminal is less than 2m above a surface to which people
have access then a guard must be fitted. he guard must be
evenly spaced about the terminal and fixed with plated screws.
A ype K2 guard is available from ower Flue Components, Vale
Rise, onbridge, N9 1 B.
6.1 he appliance does not require a separate vent for
combustion air.
6.2 he appliance can be fitted in a cupboard with no vents for
cooling but the minimum clearances must be increased to those
given below (note the clearances at the front are for a removable
panel e.g. a door).
6.3 If the appliance is to be fitted in a cupboard or compartments
with less clearance than those above (minimum clearances given
in Section 4. Siting he Appliance) then permanent vents for
cooling are required. One at high level and one at low level, either
direct to outside air or to a room. Both vents must pass to the
same room or be on the same wall to the outside air.
6.4 he minimum free areas required are:
6. Air Supply5. lue terminal positions
7
L
L
K
K
F
F
G
A
M
EJF
HI
D
G
A
B,C
Fig. 7. Siting of the fl e terminal.
ERMINAL POSI ION MIN. DIS ANCE
A– Directly below an openable window or
other opening e.g. air brick. 300 mm
B– Below gutters, soil pipes or drain pipes. 75 mm
C– Below eaves. 200 mm
D– Below balconies or car port roof. 200 mm
E– From vertical drain pipes and soil pipes. 75 mm
F– From internal or external corners. 300 mm
G– Above ground, roof or balcony level. 300 mm
H– From a surface facing a terminal. 600 mm
I– From a terminal facing a terminal 1200 mm
J– From an opening in a car port (e.g. door
window) into dwelling. 1200 mm
K– Vertically from a terminal on the same
wall. 1500 mm
L– Horizontally from a terminal on the same
wall. 300 mm
M– From door, window or air vent (achieve
where possible). 300 mm
Above the urret 30mm 30mm
In front 75mm 250mm
Below 200mm 200mm
Right-hand side 10mm 75mm
Left-hand side 10mm 75mm
POSI ION OF AIR FROM AIR DIREC
AIR VEN S HE ROOM FROM OU SIDE
HIGH LEVEL 315cm2158cm2
LOW LEVEL 315cm2158cm2
NG LPG

he system must comply with requirements of BS6798 and
BS5449 and must not be operated without being full of water
and correctly pressurised. Refer to Fig 8.
he pressure relief valve will operate at 3 bar. he discharge pipe
must be directed away from any electrics or from where it might
be a hazard.
he expansion vessel, to BS4814, has a capacity of 8 litres
charged to 0.5 bar, which is suitable for a static head of 5 metres.
A schraider type valve allows the pressure to be increased if the
static head is greater than 5 metres.
If the expansion vessel fails then it must be replaced with the
designated spare part.
Refer to BS 7074:1, BS5449 and able 9 for a guide to the
available system capacity.
he maximum system design pressure is 1.5 bar. If the pressure
is above 2.65 bar when the appliance is at maximum
temperature then another expansion vessel must be fitted as
near to the appliance as possible in the return pipe. he pressure
gauge shows the system pressure.
Fill and pressurise the system through a WRc approved filling kit.
Refer to Fig 9.
he system and the appliance must be properly vented.
Repeated venting loses water from the system, which must be
replaced. he make-up connection must be close to the
appliance in the heating return pipe through an approved non-
return valve. Refer to Fig 10.
he connection to the mains water supply must have the
approval of the local Water Company.
he integral by-pass is not adjustable.
he pump is set at maximum and should not be adjusted.
All connections in the system must withstand a pressure of up to
3 bar.
he radiator valves must confirm to BS 2767:10 and other valves
to BS1010.
Open Vent System
This appliance is NOT s itable for connection to an open vent
system.
7. Sealed System
8
Fig. 8. Sealed primary water system.
Lockshield
valve
Radiator
valve
Heating
return
Hot water out
Water main
British Standard
stop valve.
Fixed spindle type
NOTE: A drain cock should be installed at the
lowest point of the heating circuit and beneath the
appliance.
Mains cold
water
Heating
flow
APPLIANCE
Refer to
'Water Flow
Diagram'
Fig.2.
Fig 9 - System Fill Fig 10 - System make p
1.Central Heating Return
2.Auto Air vent
3.Non-return Valve
4.Make-up Vessel
5.Stop Cock
6.Fill Point
4
1
2
3
5
6
300mm Above
the highest point
of the system

It may be necessary to contact the local Water Company before
connecting the appliance.
Devices, which would prevent the flow of expansion water, must
not be fitted unless separate arrangements have been made. A
mini-expansion vessel kit is available as an optional extra.
he last 600mm of mains water pipe before the appliance must
be in copper.
he domestic hot water circuit of the appliance is suitable for a
mains pressure of up to 10 bar. A pressure reducing valve must
be fitted if necessary.
A mains water supply isolating valve is fitted.
he maximum hot water flow rate is set at the factory to 10
l/min [28Si] or 9 l/min [25Si] giving a nominal temperature rise
of 40°C with the temperature control at maximum. Refer to able
6. he temperature rise, up to the maximum set by the user is
automatically maintained by the modulation of the heat input.
In winter it may be necessary to reduce the water flow at the tap
or shower to maintain the required delivery temperature.
It is recommended that long pipe runs to taps or showers are
insulated to prevent the rapid cooling of the water.
Hot and cold taps and mixing valves must be suitable for the
available mains pressure. If necessary, a pressure reducing valve
should be fitted.
No anti-syphonage arrangements are necessary for fixed head
showers.
he hose of a loose-head shower must be fixed so that the
shower head cannot get closer than 25mm to the top edge of the
bath to prevent its immersion in the water. Alternatively the
shower can be fitted with an anti-syphonage device at the
flexible hose connection.
hermostatically controlled or pressure balancing shower valves
should be used where possible to give extra comfort and guard
against extreme temperature.
Hot and cold mains water direct to a bidet is, subject to the
approval of the local water company, permissible provided that
the bidet is of the overrim flushing type. he outlets must be
shrouded and unable to be fitted with a hand-held spray. No anti-
syphon arrangements are needed.
LIME SCALE: In areas of temporary hardness [ greater than
200ppm of calcium bicarbonate] it is suggested that a
proprietary scale reducer is fitted in the mains cold water
connection to the appliance. Installation of a scale inhibitor
assembly should be in accordance with the requirements of the
local Water Company. An isolating valve should be fitted to allow
servicing. he water hardness can be determined by reference to
the local Water Company.
he appliance requires a maximum of 3.38 m3/h of natural gas
(G20) or 1.2 m3/h of propane (G31) [28Si] or 2.98 m3/h of natural
gas (G20) or 1.25 m3/h of propane (G31) [25Si]. Refer to able 7.
A natural gas appliance must be connected to a governed meter.
he installation and connection of the gas supply to the
appliance must be in accordance with BS6891.
he meter (NG) and the pipework to the appliance must be
checked, preferably by the gas supplier, to ensure that a
dynamic pressure of 20mbar for natural gas and 37mbar for
propane is available at the appliance [equivalent to about
18mbar or 35mbar at the gas valve inlet pressure connection]
and that the gas flow is adequate for all the installed gas
appliances operating together.
Mains supply: 230V ~ 50 Hz 180watts. External fuse 3A.
Internal fuses F1-2A, F2-1.6A (20mm). Spare internal fuses are
supplied with the appliance. Refer to Fig 13.
he appliance must be earthed and it must be possible to
completely isolate the appliance.
he mains cable must be 0.75mm2(24x0.20 mm) to BS6500 -
able 15 or 16.
he mains cable must be connected to the terminal S 12
marked L (red or brown lead), N (black or blue lead) and the
Earth stud (green or green/yellow lead) and secured with the
cable clamp. he Earth lead must be still be slack when the other
leads are taut. Refer to Fig 14.
he connection to the mains must be either : A 3A fused three-
pin plug and unswitched socket outlet (both complying with
BS1363) or a double pole isolator with a contact separation of
3mm in all poles and supplying the appliance and controls only.
A room thermostat or an externally mounted programmer must
be suitable for mains voltage operation, the leads must be
securely fixed in the cable clamps. Only do ble ins lated mains
voltage controls not req iring an earth lead may be sed. he
control board is accessed by removing the controls connections
cover. Refer to Fig 29.
A programmer or clock is available to fit into the facia. Full
instructions are sent with the control.
On very rare occasions an external frost thermostat might be
considered where parts of the system are remote from the
appliance. Refer to WHS echnical Department for more
information, el: 08705 266241.
Safety Check: If there is an electrical fault after installation check
for fuse failure, short circuits, incorrect polarity of connections,
earth continuity or resistance to earth.
10. Electrical
8. Domestic Hot Water
9
9. Gas Supply

10
Fig. 11. Wiring diagram.
Fan
Flame sense
electrode
Air
pressure switch
Spark
electrode
Spark
transformer
Mains in
Link
Control Board
CH sensor
(front of heat
exchanger)
Flow
switch
S 16
2 blue
2 orange
2 brown
brown
blue
blue
brown
2 violet
white
2 red
2 yellow
2
pink
S 12 S 8 S 15 S 1
Pump
Gas valve
Reg
Main
Main
2 green
brown
yellow
Overheat cut-off
device
DHW sensor

11
Fig. 12. F nctional flow diagram.
Mains
indicator
On/Off
switch
S 8
(LS)
S 8
(LR)
S 8
(NS)
S 1
Centre
Pin
S 15
Pin L
REL 1 REL 3
Pump
Fan
S 12 Pin N
Optional link
Room
thermostat
ransformer
Fuse F2 (1.6A
Slow)
Fuse F1
(2A Slow)
N
N
S 12 Pin L
LIVE
IN
green
Electronics
Electronics
Electronics
Inputs
Outputs
Spark Indicators
Settings
Regulator valve
CH
demand
indicator
Red
Spark
electrodes
DHW
demand
indicator
Red
Flame
detect
indicator
Red
Main valve
Main valve
Flow switch CH sensor
DHW sensor
Air pressure switch
Flame sense
Overheat cut-off
24V programmer
Reset button
Gas valve mode switch
CH pressure adjust pot
CH Control knob
DHW control knob
Convert AC to low
voltage electronics
Electronics/
microprocessor
(Safety Low Voltage)

Note: READ HIS SEC ION FULLY BEFORE COMMENCING HE
INS ALLA ION
11.1 General
he appliance is only suitable for fitting to a sealed system.
he flue must be installed as specified in BS5440:1.
11.2 Unpacking
Remove the appliance from its packaging and check the contents
against the packing list.
Lie the appliance on its back and undo the union connections on
the manifold assembly. Refer to Fig 16. Slide the appliance off the
wall mounting assembly.
11.3 Site Preparation
Check that the correct position for the appliance has been
chosen. Refer to Section 4 and able 8.
Check that the wall is flat and will support the weight of the
appliance. Refer to able 4.
11.4 Fixing Holes and Flue Opening
Hold the wall mounting assembly against the wall. Check that
the assembly is level. he diamond cut-out on the assembly
indicates the centre-line of the appliance.
Mark the position of the fixing holes and the flue opening. Refer
to Fig. 5 and 15.
Mark the centrelines of the pipe connections to aid the pre-
plumbing of the system pipework.
Check the position of the fixing points and flue opening before
drilling the fixing holes 60mm deep for the No. 12 size plugs and
cutting the flue duct hole at 110mm diameter [150mm diameter
for internally fitted flues].
11.5 Wall Mounting Plate and Manifold
Fit the plugs and insert the bottom screws. Offer the assembly to
the wall utilising the keyhole slots on the manifold assembly and
fix to the wall. Refer to Fig 15 and 16.
Check that the assembly is properly aligned before tightening
the screws.
11.6 Gas and Water Pipes
Remove the gas cock and fix the appropriate fitting to connect
the inlet pipe and refit. Refer Fig 16.
Pre-plumbing is not recommended if no movement in the pipes
is available.
If it is necessary for any of the pipes to run up the back of the
appliance then they must be arranged to pass behind the
expansion vessel. Refer to Fig 3. Pipework must not run
horizontally within the limits of the casing.
Support the valves when tightening the connections to prevent
distortion of the manifold assembly
It is important that the pipes are not fixed near the appliance
using clips that put a strain on the connections.
Before the appliance is fitted to the wall thoro ghly
fl sh the system and mains water s pply.
11. Installing The Appliance
12
Fig 13 - Replacement internal f ses
1
2
3
4
5
1. Fuse -F1 2A 5. Clip on Facia cover
2. Fuse -F2 1.6A
3. Connections Cover
4. Connections Cover Fixing
Screw
NOTE: Check the size of the fuse before fitting
Earth
Green/Yellow
Blue
Neutral
Blue
LN
Fig.14 . Mains electricity connections.
230V
ST12
LR
E
Bottom Left Hand Side - Facia
Strain relief clamp
NLS
Live
Brown
Mains lead
External control
Note: When the mains ON/OFF switch on the facia is turned
OFF the 2amp fuse is still live. Refer to Fig.12.
Fig.15 . Wall mo nting assembly
20
▲
▲
218
▲
▲
75
540
▲
▲
▲
▲
▲
▲
60
60
65
338
797
Cabinet Height
800
367
All dimensions in mm

11.7 Install the Boiler
Remove the cabinet by unscrewing the screw at the top front
and releasing the sides. Lift from the top location. Refer to Fig.
18.
Check that the gas and water valves are closed. Refer to Fig.16.
Fit the new seals, in the hardware pack, to the service valves on
the manifold.
Lift the appliance to the wall, engage in the top support and
lower onto the manifold assembly. ighten the gas and water
connections.
Fit a discharge pipe to the relief valve leading it away from any
electrics or where it might be a hazard. Lower the facia to gain
access. he pipe must not be less than 15mm in diameter and
must run continuously downward outside the appliance. Refer to
Fig 17.
11.8 Air and Flue Duct Preparation
he method of installation of the flue system may be varied to
suit the actual site conditions. he instructions for connecting
and fixing the ducts must, however, be strictly followed.
Remove all packing material from the flue components.
Fit the flue restrictor ring by unscrewing and removing the flue
spigot from the boiler. Refer to Fig.19.
Restrictor Size 79mm to all Horizontal and Vertical flues
upto 725mm long.
he standard telescopic flue assembly is suitable (without
cutting) for flues from 425mm up to 725mm measured from the
centre-line of the boiler flue outlet to the outer face of the wall.
Refer to Fig.20.
he minimum length of the standard flue, after cutting is
330mm.
13
65 65 65 65
Wall
Frame
Wall
Frame
CH
Flow DHW
Flow
Gas
DHW
Cold
Inlet CH
Return
Fibre
Washer
Fig.16 . Manifold assembly
All dimensions in mm
Fig.17 . Relief valve drain connection
Pump
Relief Valve
Drain
Connection
(push fit)
Boiler
Drain
Pressure
Gauge
Capillary Relief
Valve
Fig.18. Inner case and facia fixing
Inner
case
cover
Facia panel
fixing screws
(2)
0I
Facia
Fixing screws
(4)
Fig.19. Fl e spigot and restrictor 1
2
3
4
1. Flue spigot fixing screws
2. Flue spigot
3. Restrictor ring
4. Flue spigot fixing holes
Position of
the cabinet
fixing screw

If L is greater than 725mm then extension duct kit/s will be
required - each kit extends the flue by 750mm up to a maximum
of 2975mm. See table below.
EX ENSION MAXIMUM FLUE LENG H mm
1 1475
2 2225
3 2975
11.9 Measure and Cut the Ducts.
General: Cut the ducts as necessary, ensuring that the ducts are
square and free from burrs. Always check the dimensions before
cutting.
Measure the distance L. Refer to Fig. 22 and 23.
he standard flue can be telescopically adjusted to any length
between 425mm and 725mm measured from the centre of the
turret.
Fix the flue assembly together using the self-tapping screws
provided. Refer to Fig. 20.
It will only be necessary to cut the standard assembly if L is less
than 425mm. Cut the flue turret assembly and the terminal
assembly by the same amount i.e L=350 - remove 75mm from
each assembly.
Minimum side flue length = 330mm (accommodating a
10mm Service clearance and a 100mm wall)
Minimum rear flue length = 330mm (accommodating a
100mm wall)
If L is between 1175 - 1475mm (1 extension)
1925 - 2225mm (2 extension)
2675 - 2975mm (3 extension)
it is not necessary to cut the ducts.
If L is between 725 - 1175mm (1 extension)
1475 - 1925mm (2 extension)
2225 - 2675mm (3 extension)
It is necessary to shorten the assembly by cutting the first
extension duct assembly i.e. L = 1000mm - remove 175mm
from the air and flue ducts.
14
Fig.20. Standard fl e assembly
L
Fixing screw
Flue
turret
assembly
Appliance casing
elescopic adjustment
erminal
assembly
Fig.21. Extension d ct
L
Fixing screw
Flue
turret
assembly
Appliance casing
erminal
assembly
Fixing screw
Ducts of equal length
Fig.22. Fl e d ct length - side
L
Flue
turret
assembly
erminal
assembly

NO E: Extension duct measurements do not include the
socketed end. Unless specifically instructed the socketed end
must not be removed.
Fix the flue ducts together before fixing the surrounding air duct,
the cut ducts fit into the flue assembly.
11.10 Fitting the Flue Assembly with Access to the erminal.
Prepare the flue duct assembly as described in Section 11.8.
Apply the plastic tape to the air duct in contact with the external
brickwork.
From inside push the assembly through the wall. Align the flue
turret and push fully onto the spigot on the appliance. ighten
the clamping ring and fix with the screw provided. Refer to
Fig.24.
Make good the internal wall face and the external brickwork or
rendering.
11.11 Fitting of the Flue Assembly without access to the erminal.
A rubber gasket kit is available from Worcester Heat Systems.
NO E: A larger diameter opening in the wall is required. Refer to
able 2.
Prepare the flue assembly as described in Section 11.8.
Fit the rubber sealing gasket centrally onto the terminal
assembly and tighten the clamp. Refer to Fig. 25.
Apply the plastic tape to the air duct in contact with the external
brickwork.
From inside push the assembly through the wall so that the
gasket flange is against the outer face. Refer to Fig. 25.
It may be necessary to adjust the legs of the flue centering ring.
Align the flue turret and push fully onto the socket on the
appliance. ighten the clamping ring and fix with the screw
provided. Refer to Fig. 24.
Seal the gap around the duct at the inner wall face with the
flexible seal provided and make good.
11.12 Flue Bends.
90° and 45° bends are available. A maximum of two bends may
be used in addition to the first bend on the flue turret.
A 90° bend is equivalent to 1m of straight duct.
A 45° bend is equivalent to 0.5m of straight duct.
A maximum flue assembly of 2m is possible with 1 X 90° bend
and 1m with 2 X 90° bends.
Measure the lengths X,Y and Z. Refer to Fig.26.
he maximum value of X using the turret assembly only is
506mm. Reduce the ducts to the appropriate length i.e. X =
406mm, cut 100mm from the air duct and 120mm (to cover the
entry into the 45° or 90° elbow) from the flue duct. Refer to
Fig.27.
NO E: he flue system ducts between the elbows, dimension Y,
requires the socketed ends (of the first extension if two or more
are used) to be removed and the air and flue tubes to be cut to
the same length.
Cut the ducts to a length Y - 162mm. Refer to Fig.26.
he final section, dimension Z, of the flue system must include a
section of plain duct assembly i.e . an extension assembly with
the sockets removed. Reduce the final section, including the
terminal assembly, by the appropriate amount i.e. Air duct Z -
81mm and the flue duct Z - 51mm. Refer to Fig.26.
If Z is less than 425mm it will be necessary to cut the air and flue
ducts of the extension to a plain length of 100mm and reduce
the length of the terminal assembly i.e Z=350mm - remove
75mm from the terminal assembly.
If Z is 425 - 725mm it is not necessary to cut the terminal
assembly or use a second extension duct as the length can be
set telescopically.
If Z is greater than 725mm then two extension duct assemblies
will be required, the first assembly being cut to length as plain
tubes.
15
Flue
turret
assembly
erminal
assembly
Fig.24 . Fl e T rret Fixing
1
2
3
1. Flue turret assembly
2. Clamp
3. Appliance
4. Fixing Screw
Fig.23. Fl e d ct length - rear
Fig.25 . Terminal assembly for internal
fitting of the fl e.
Flue centering ring
Flue erminal
Rubber sealing
gasket
Clamping ring
Flue terminal
Air duct
Flue duct
Rubber sealing gasket
Fixing clamp
L
4

If more than two extension ducts are needed in any section to
achieve the required length then the final section of the
assembly must not be less than 325mm without cutting the
terminal assembly.
NO E: he flue duct of the final extension must be 30mm longer
than the air duct.
Each section must be connected to the previous section of the
flue bend by fixing the flue ducts together and then similarly
fixing the air ducts which engage the elbows.
Fit the assembly as described in Section 11.9, 11.10 as
appropriate.
Make good the internal and external brickwork or rendering.
11.13 Vertical Adapter for Horizontal Flues.
An adapter is available for an initial short section of vertical flue.
Refer to Fig. 28.
Measure and cut the flue as described in Section 11.11.
he first, vertical, section (equivalent to dimension X) is
measured from the top of the boiler casing. Cut the vertical
section of the extension duct to 167mm less than the measured
distance. Do not remove the socketed ends.
he minimum measured distance is 167mm.
Seal the air duct to the spigot using silicone sealant.
Fix the adaptor with the clamp and screw provided.
11.14 Completion of the Installation.
Check that all the connections on the manifold have been
tightened. Refer to Fig.6.
Remove the facia bottom panel. Refer to Fig.29.
Connect the mains electricity supply lead to the appliance and
secure the cable clamp. Refer to Fig.14.
Check there is sufficient loose lead to allow the release of the
facia panel assembly and that the earth lead of the mains supply
cable is longer than the live and neutral leads.
Fit the facia mounted programmer if applicable. Refer to Fig.31.
Connect any external controls ensuring that the leads pass
through the appropriate clamps. refer to Fig.32.
est for gas soundness as described in BS6891.
If the appliance is not commissioned immediately, replace the
cabinet and facia bottom panel. Check that the gas and
electricity services have been turned off.
16
Fig.26. Fl e bends
X
Z
Y
Y-162
Plain tube
120mm
100mm
Fig.27 - Elbow to Fl e T rret
Assembly.
Fig.28 Vertical Adapter.
Flue Duct
Air Duct
Adapter
Flue Spigot
Flue urret
Bend
Clamp

17
Fig.29. Facia connections cover
Facia
Controls
connections
cover
Fixing screw Facia bottom panel
(clip-on)
Fig.30. Programmer cover Cover panel
Facia
Programmer
connections
Fig.33. Facia connections
1 2 34 5 67
8
9
10
1. Earth screw
2. Mains connection (L N)
3. Fuse F1
4. Mains voltage room thermostat/external control-mains
voltage S 8
5. Fuse F2
6. Controls 24V - S 13
7. Mains harness S 16
8. Fan S 1
9. Pump S 5
10. Earth tag
11. Cable clamps (threaded)
11
Fig.31. Programmer connection
Facia
Programmer
connector
Programmer
connections
Clip
Programmer Pressure gauge
Control
board
Fig 32 - Mains Voltage External Controls Connections
230 V Room hermostat Connections
Ns Ls LR
S 8
Ns Ls LR
S 8
Remove Link
Neutral
Live
Switched Live
Neutral
Live
Switched Live
Motor
230 V Programmer Connections
230 V room thermostat and
Programmer Connections
Ns Ls LR
S 8
Neutral
Live
Neutral
Live
Switched Live
Motor
Switched Live
Series
connection
to be made
safe
NOTE: Only double insulated controls not requiring an earth can be used
Remove Link

Benchmark Water Treatment: For optim m performance after
installation, this boiler and its associated central heating
system sho ld be fl shed in accordance with the g idelines
given in BS7593:1992 - Treatment of water in domestic hot
water systems. F ll instr ctions are s pplied with proprietary
cleansers sold for this p rpose. If an inhibitor is to be sed
after fl shing, it sho ld be sed in accordance with the
inhibitor man fact rers instr ctions.
S itable fl shing agents and inhibitors are available from Betz
Dearborn Tel: [phone] and Fernox Tel: [phone].
Instr ctions for se are s pplied with these prod cts.
12.1 Remove the appliance cabinet by removing the screw at
the top centre of the cabinet.
Check that the electrical supply and the gas supply to the
appliance are turned off and that all the water connections
throughout the system are tight.
Open the system valves at the appliance. Refer to Fig.6.
Open all the radiator valves. Remove the automatic air vent cap.
Refer to Fig. 34.
Fill the system through the external filling loop. Refer to Section
7, Sealed System.
Vent each radiator in turn. he automatic air vent will vent the
appliance. Refer to Fig 34.
Remove the cap from the pump and turn the shaft about half a
turn. Replace the cap. Refer to Fig 35.
Check that the pressure relief valve operates by turning the knob
anti-clockwise until it releases. Lower the facia to gain access to
the relief valve. Refer to Fig 17. Water should be expelled from
the discharge pipe.
12.2 Set the Expansion Vessel Pressure
he charge pressure of the expansion vessel as dispatched is
0.5bar, which is equivalent to a static head of 5m [17ft]. he
charge pressure must not be less than the static head at the
point of connection. A Schraeder type valve is fitted to the
expansion vessel to allow the charge pressure to be increased if
necessary. Refer to Fig 34. he expansion vessel must be charged
to 0.35bar less than the initial system design pressure.
Note: 1bar = 10.2m = 33.5ft of water.
12.3 Set the System Pressure
Fill the system until the pressure gauge is at 2.5bar and check for
leaks.
Release water from the system using the relief valve test knob
until the required system pressure is obtained, upto a maximum
of 1.5bar.
Set the pointer on the pressure gauge to record the set system
pressure.
If the pressure indicated on the gauge is greater than 2.65bar
when operating at the maximum central heating temperature,
an extra expansion vessel must be fitted to the system as close
as possible to the appliance central heating return connection.
he appliance [as despatched] can accommodate a system
volume of 100 litres with a system pressure of 0.5bar. Refer to
BS7074 Part 1, BS5449 and able 8. If the system volume is
greater then an extra vessel must be fitted as close as possible to
the appliance central heating return connection and pressurised
to the same figure as the integral vessel.
12.4 Clock/Programmer: he controls fitted to the appliance
should be set up at this stage.
12.5 Check that the gas and electricity supplies are turned off.
Connect a pressure gauge to the gas valve burner pressure test
point. Refer to Fig 36.
12. Commissioning The Appliance
18
Fig.34. A tomatic air vent and comb stion
test point
Fig. 35. P mp venting.
Pump
Pump cap
Electrical
connections
cover
Fig. 36. Gas valve.
Modulating
solenoid
valve
Burner pres-
sure test
point
Burner con-
nection
Safety sole-
noid valves
Gas
Inlet pressure
test point
Minimum
pressure
adjustment
screw
Maximum
pressure
adjustment
screw
Automatic air vent
Flue connections
Expansion vessel charg-
ing point
Expansion vessel
Wall mounting frame
Combustion products
test point (front cap)

Remove the clip-on facia bottom cover and controls connections
cover. Refer to Fig 29.
Slide down the access panel to display the mode switch and the
adjusting tool. Refer to Fig 37.
12.6 Checking the Burner Pressure
Check that all the radiator valves are open.
Check that the system is pressurised and set to the required
pressure as indicated on the gauge.
Set the temperature control knobs to maximum and the
clock/programmer to operate continuously.
urn on the gas and electricity supplies.
Set the mode switch to MAX using the mode adjuster tool. Refer
to Fig 37 and 38. NOTE: Two red lights will flash rapidly on the
facia.
A continuous spark will occur until the burner is alight and
sensed by the control circuit. he burner will remain at its
maximum domestic hot water pressure for one minute. Refer to
able 1.
It should not be necessary for the gas valve to be adjusted.
Note: he burner pressure is factory set and if, after checking
that the dynamic (working) supply pressure is sufficient i.e.
18.0mb (NG) approx, or 36mb (LPG) at the gas valve inlet
pressure test point, the correct pressure cannot be obtained then
Worcester Heat Systems Service Department should be
contacted.
If the appliance does not light then check that it is not in the
‘lock-out’ state by pressing the reset button. Refer to Fig 39.
Set the mode switch to Normal.
he burner pressure will drop to the minimum setting and will
ramp up to the maximum central heating pressure appropriate
to the appliance and the gas. Refer to able 1. It should not be
necessary for the central heating potentiometer to be adjusted to
change the burner pressure. If adjustment is required then the
adjusting tool is used to alter the setting of the potentiometer.
Refer to Fig 38.
Set the mode switch to MIN. NOTE: Two red lights will flash
rapidly on the facia.
he burner pressure will drop to the minimum pressure
appropriate to the appliance and the gas for both the central
heating and domestic hot water modes. Refer to able 1. It
should not be necessary for the central heating potentiometer to
be adjusted.
est for gas soundness at the joint between the burner and the
gas valve with leak detection fluid.
Set the mode switch back to Normal.
urn the electricity supply off and then back on to reset the controls.
Replace the facia cover panels.
12.7 Domestic Hot Water
urn the central heating temperature control knob fully anti-
clockwise. Refer to Fig. 39.
Open a hot tap near the appliance. he burner will light and go
to the maximum burner pressure appropriate to the appliance
and the gas . Refer to able 1.
Gradually close the tap and check that the burner pressure falls.
Fully open the tap and check that the pressure rises.
Close the tap and check that the burner goes out.
he fan may continue running until the appliance has cooled to a
pre-set temperature.
12.8 Central Heating
Check that all the radiator valves are open.
Check that the system is pressurised and set to the required
pressure as indicated on the gauge.
Check that the clock/programmer is set to operate continuously.
Set the room thermostat and the central heating temperature
control to maximum.
he burner will light and the appliance will modulate its output
from minimum to maximum over a period of about two minutes.
Check that all the radiators are heating up evenly.
Shut down all but one of the radiators and observe the burner
pressure fall. Open all the radiators and check that the burner
pressure rises.
12.9 Balance the system to give a temperature differential of
11°C. A non-adjustable by-pass is fitted to the appliance.
12.10 Set the room thermostat to minimum and check that the
burner goes out. Reset the room thermostat to maximum and
the burner will re-light and follow the normal operating
procedure.
urn off the gas service cock. he burner will go out but sparking
from the electrode will continue for 10 seconds when the
appliance will ‘lock-out’. After 60 seconds carefully open the gas
service cock, press the reset button and observe the burner re-
light and follow the normal sequence of operation. Refer to Fig 6 and 39.
urn off the gas service cock and the electricity supply to the
appliance.
Drain the system while the appliance is hot.
Refill, vent and re-pressurise the system as described in Section
12.1 preceding, adding, if necessary, a suitable proprietary
inhibitor. Further information is available from Betz Dearborn
0151 420 9563 or Fernox 01799 550811.
12.11 Domestic Hot Water and Central Heating
Set all controls to maximum.
urn on the electricity supply to the appliance and open the gas
service cock at the appliance.
he burner will light and heat will pass into the system. urn on
a hot tap and check that hot water is soon discharged from the
tap. Close the tap.
he appliance will then return to the central heating mode and
automatically balance with the system requirements.
urn off the appliance.
12.12 Completion of Commissioning
Disconnect the pressure gauge and tighten the test point screw.
Restart the appliance and check for gas soundness around the
test point screw.
Refit the cabinet.
19
Fig.37. Mode control cover
Fig.38. Mode adj stment
Facia
Mode adjuster
Mode adjustment cover
Max/Min switch
Central heating limit
potentiometer
Not operational

If the appliance is to be passed over to the user immediately
then set the controls to the users requirements.
If the appliance is to be left inoperative in frosty conditions then
set the programmer, if fitted, to off. Do not turn the electricity or
gas supplies off. he appliance will operate under the control of
the integral frost protection facility.
If there is any possibility of the appliance being left totally
unused in freezing conditions then switch off the gas and
electricity and drain the appliance and the system.
13.1 Hand over the User Booklet.
13.2 Explain how to operate the appliance safely and efficiently.
13.3 ell the user what to do if the appliance is not to be used in
very cold conditions.
13.4 ell the user what to do if the system pressure falls.
13.5 Explain that regular servicing will maintain the safe and
efficient operation and extend the life of the appliance. WHS can
offer a comprehensive maintenance contract.
13.6 ell the user that any work on the appliance must only be
carried out by a competent, CORGI registered, person.
13.7 Complete and hand over to the ser the Benchmark
Log-Book.
14.1 he extent of the service is determined by the operating
condition of the appliance when tested by a competent person.
It is the law that any service work is carried out by a competent
CORGI registered person.
14.2 Inspection
Check that the terminal and the terminal guard, if fitted, are clear
and undamaged.
If the appliance is in a compartment or cupboard check that the
specified service space around the appliance is clear. Refer to able 8.
Check all the joints and connections in the system and remake
any that show signs of leakage. Refill and re-pressurise as
described in Section 12-Commissioning.
Operate the appliance and take note of any irregularities. Refer to
Section 18-Fault Finding for rectification procedures.
Check the combustion performance
Remove the cap from the sample point on the top of the
appliance. Refer to Fig 34.
Connect the sampling meter.
With the appliance at maximum rate and stable in the DHW
mode expect readings of NG 5.5 - 8.5% CO2, 0.002 - 0.015% CO.
hese figures cover all flue conditions.
Refit the cap after the test.
Disconnect the electrical supply at the mains and turn off the
gas supply at the gas service cock on the appliance before
starting any service procedures.
Always test for gas soundness after the service has been
completed.
14.3 Component Access
o service the appliance it may be necessary to remove some or
all of the following parts to gain access to components which
may need to be checked or replaced.
Cabinet Unscrew the screw at the top of the cabinet, release
the sides. Lift up and away from the top locating
pegs.
Facia Panel Unscrew the two screws and lower. Refer to Fig 40.
Inner Case Cover Unscrew the four fixing screws and remove
the cover. Refer to Fig 40.
Comb stion Chamber Unscrew the two screws at the top and
the two wing nut extended screws at the sides, pull
forward and remove. Refer to Fig 41.
Fan Carefully pull off the electrical connections and the
tubes from the airflow-sensing device. Unscrew the
four screws and remove the fan assembly. Refer to
Fig 42.
Fl e Hood Remove the fan. Unscrew the four screws and
remove the hood. Refer to Fig 43.
B rner Remove the combustion chamber. Carefully pull off
the connections to the spark and flame sensing
electrodes. Release the union nut beneath the
burner and remove. Refer to Fig 44.
14.4 Component Cleaning
Only use a non-metallic brush to clean components.
Clean the fan taking care not to block air flow detector.
Clean the burner to ensure that the blades and injectors are clear.
Do not us a metal probe to clean the injectors.
Clean the electrodes, replace if there is any sign of deterioration.
Clean the heat exchanger. Cover the gas inlet tube and remove
any deposits from the heat exchanger from the top and bottom.
Carefully straighten any distorted fins on the heat exchanger.
Check the combustion chamber insulation and replace if there is
any sign of damage or deterioration. Refer to Section 15.4.5.
Clean the controls in situ using a non-metallic brush.
Carefully refit any components removed in the reverse order.
Check that all screws are tight and the connections properly
remade with the appropriate gaskets/O-rings.
Re-commission, as necessary, for correct operation to the users
requirements. Refer to Section 12 Commissioning.
14. Inspection And Service
13. Handover
20
Fig.40. Inner case and facia fixing
Inner
case
cover
Facia panel
fixing screws
(2)
0I
Facia
Fixing screws
(4)
0I
Fig. 39. Facia controls
Mains
ON/OFF
Switch
Power ON
Indicator
Central Heating
Operation and
emperature
Control Knob
Domestic
Hot Water
emperature Control
Knob
Central Heating
Indicator
Light
Domestic Hot
Water Indicator
Light
Burner
Operation Light
System
Pressure
Gauge
Reset
Button
!