Potterton PRIMA 30C User manual

30C, 40C, 50C & 60C
open flue gas fired boiler
FOR USE WITH NATURAL GAS (G20) ONLY
Read these instructions thoroughly before working on the boiler.
Leave the instructions adjacent to the gas meter.

2
GENERAL - Page 2
GAD (90/396/EEC)
POTTERTON PRIMA 30C G.C. No. 41.605.90
POTTERTON PRIMA 40C G.C. No. 41.605.91
POTTERTON PRIMA 50C G.C. No. 41.605.92
POTTERTON PRIMA 60C G.C. No. 41.605.93
IMPORTANT
This appliance must be installed by a competent person as stated in the Gas Safety (Installation and Use) Regulations 1994.
Prima boilers are certified for safety, it is therefore important that no external control devices (eg. flue dampers, economisers
etc.) be directly connected to these appliances unless covered by these installation instructions or otherwise recommended
in writing. Any direct connection of a control device not approved by Potterton Myson could invalidate the certification and
the normal warranty.
LIST OF CONTENTS
General Page No. 2 Installation Instructions Page No.13
Accessories Page No. 3 Commissioning Page No.19
Installation Data Page No. 3 Servicing Instructions Page No.21
Boiler Dimensions Page No. 3 Health and Safety Information Back Page
Site Requirements Page No. 5 Control Systems }Supplied in
Technical Data Page No. 7 Pipework and Wiring Guide }Literature pack
Users Instructions }
GENERAL
Once the pilot has been lit Potterton Prima C boilers are
automatic in operation. They are wall mounted natural
draught open flue appliances using a cast iron heat
exchanger and are available in four outputs ranging from
5.86-17.58kW (20,000-60,000 Btu/h).
The boilers which are designed to provide domestic hot
water and/or central heating must be used on INDIRECT hot
water systems only.
The cast iron heat exchanger is suitable for use on open
vented gravity hot water/ pumped central systems or fully
pumped systems which may be sealed or open vented.

3
ACCESSORIES - Page 3
The following range of Potterton Myson system controls are
also available and further information will be provided on
request.
Electronic Programmer EP2001, EP3001, EP4001, EP5001
and EP6000.
Programmable Electronic Thermostat PET1
Thermostatic Radiator Valve.
Electronic Cylinder Thermostat PTT2 or PTT100
Electronic Room Thermostat PRT2 or PRT100
Motorised Zone Valve MSV222 or MSV228
Motorised Diverter Valve MSV322
INSTALLATION DATA - Page 3
The installation of the boiler must be in accordance with the
latest relevant requirements of the Gas Safety (Installation
and Use) Regulations 1994, local building regulations, IEE
Wiring Regulations and the byelaws of the local Water
Undertaking.
Detailed recommendations are contained in the following
British Standard Codes of Practice:-
BS6798. BS5440 Part 1.
BS5440 Part 2. BS55449 Part 1.
BS5546, BS4814,
BS6891 BUILDING REGULATIONS.
MODEL WATER BYELAWS.
BRITISH GAS PUBLICATION DM2.
GAS SAFETY (INSTALLATION AND USE) REGULATIONS
1994.
BUILDING STANDARDS (SCOTLAND)
REGULATIONS.
BOILER DIMENSIONS - Page 3
Figure 1 BOILER DIMENSIONS (mm)

4
GENERAL ARRANGEMENT - Page 4
Figure 2 - GENERAL ARRANGEMENT

5
SITE REQUIREMENTS - Page 5
These boilers are not suitable for external installation. The
appliance must not be installed in bathrooms, shower rooms,
bedrooms, bed-sitting rooms, garages or rooms where highly
inflammable materials or vapours are likely to be present.
Fitting in toilets or cloakrooms is not recommended but is
permitted, provided the combustion air is taken direct from
outside. Where installation of the boiler will be in an unusual
location special procedures may be necessary and BS6798
gives detailed guidance in this aspect.
Ensure that the gas supply pipe and meter are large enough
for this appliance and any others that may be run off the
same meter. Reference should be made to BS6891
Boiler Mounting Surface.
The boiler must be mounted on a flat wall, which may be of
combustible material and must be sufficiently robust to take
the weight of the boiler. It is recommended that any wall
covering behind the boiler that may discolour should be
removed before mounting the boiler. The requirements of the
local authorities and the Building Regulations must be
adhered to.
IMPORTANT NOTICE:
TIMBER FRAMED HOUSES
If the appliance is to be fitted in a timber framed building, it
should be fitted in accordance with British Gas Publication
‘Operational Procedures for Customer Service’ Part 19. If in
any doubt, advice should be sought from the local region of
British Gas.
Clearances Around the Boiler
This appliance must at all times be fitted more than 100mm
(4in) above floor level.
The following minimum clearances must be maintained after
installation for correct operation and servicing of the boiler:-
610mm (2ft) at the front of the boiler.
5mm (0.2in) each side of the boiler.
100mm (4in) at the top.
100mm (4in) at the bottom where fitted above a working
surface etc.
Additional clearances to these may be required for
installation and are left to the discretion of the installer.
Combustion Air and Ventilation Requirements
General recommendations are given in BS5440 Part 2, and
the following notes are given as a general guide.
1. Ventilation of Compartments containing Gas Boilers
THE 60C IS NOT SUITABLE FOR INSTALLATION IN A
COMPARTMENT.
For other models there should be two permanent air vents,
one at low level and one at high level. Each opening,
whether left free or furnished with a grille, must have a
minimum effective area in accordance with Table 1.
TABLE 1
Level of Area for air whether taken
Air Vent from a Room or Outside
sq. in. sq. cm.
30C High 38 245
Low 38 245
40C High 52 335
Low 52 335
50C High 66 425
Low 66 425
There must be at least 300mm (l2in) clearance between the
grille on the front of the boiler casing and any internal
surface of the cupboard to allow for adequate air for
operation of the draught diverter.
Further details for installation of a boiler within a
compartment are given in BS6798.
2. Ventilation of rooms containing Gas Boilers.
The ventilation of the room containing the boiler shall include
air for combustion and draught diverter dilution. This applies
also when the boiler is sited in a compartment, unless the air
vents are both direct from outside.
A permanent air vent shall be provided in an outside wall of
the building at either high or low level.

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SITE REQUIREMENTS - Page 6
This opening may be:
aDirectly into the room or space containing the boiler or,
bVia a duct through the wall or roof of the room, (where
such a method is considered British Gas should be
consulted) or,
cInto an adjacent room or space which has an internal
permanent air vent of the same size to the room
containing the boiler. It is undesirable to ventilate via a
kitchen, bathroom or toilet.
The air vent should be sited as far as possible from any
extract fan to avoid short circuiting. To avoid the possibility of
freezing water pipes, the vent should not be sited near pipes.
The minimum effective area of the permanent air vent must
be:
30C 22 sq cm 3.4 sq in
40C 39 sq cm 6.0 sq in
50C 56 sq cm 8.7 sq in
60C 74 sq cm 11.5 sq in
If the room (e.g. kitchen) from which air is drawn, has an
extract fan fitted, then the opening size of the permanent air
vent should take this into account to ensure that the
operation of the boiler flue is not adversely affected when the
extract fan is running with all doors and windows closed.
This should be checked in accordance with BS5440 Parts 1
and 2.
3. Grilles and Ducts
Any grille and/or duct should be so sited and of a type not to
become easily blocked or flooded and should offer low
resistance to air flow.
FLUE
A 100mm (4in) internal diameter flue must be connected to
this appliance to evacuate the products of combustion from
the boiler. The flue
connecting socket on the boiler is designed to accept flue
pipe to BS567.
If a fluepipe to BS715 is to be used an adaptor must be fitted
to the boiler connecting socket.
Reference should be made to The Building Regulations and
British Standard 5440 Part 1. The following notes have been
compiled for your guidance:-
aThe flue pipe should be at least 25mm from any
combustible material, or when passing through a wall,
floor or roof, be separated from any combustible
material by a non-combustible sleeve enclosing an air
space of at least 25mm around the flue pipe.
bIdeally a flue should rise vertically to a termination point
which is unaffected by down draught or wind eddies.
Therefore, for practical purposes, the flue should have
the shortest run possible; 90° bends should be avoided.
The terminal should be at least above roof edge level
and must be of a type acceptable to British Gas.
cWherever possible there should be at least 600mm (2ft)
of vertical flue from the boiler flue socket.
Note; A split socket should be fitted in this length.
dHorizontal runs should be avoided. If a near horizontal
length is unavoidable, it must be followed by at least
twice that length of vertical flue.
eWherever possible internal stacks, lined if necessary,
should be used.
fAll brick chimneys must be lined with a liner acceptable
to British Gas.
gWhere condensation is likely a means of draining must
be provided.
hIf an existing flue is being used, ensure that it has been
thoroughly swept before lining or connecting the boiler.

7
ELECTRICITY SUPPLY - Page 7
A 240 volts ~ 50Hz. single phase electricity supply fused at
3A must be provided in accordance with the latest edition of
the lEE wiring regulations and any other local regulations
that may apply. The current rating of the wiring to the boiler
must exceed 3 amperes and have a cross sectional area of
at least 0.75mm2in accordance with BS6500 1990 Table 16.
The method of connection to the electricity supply MUST
facilitate complete isolation of the appliance, preferably by
the use of a
fused three pin plug and unswitched, shuttered socket outlet,
both complying with the requirements of BS1363.
Alternatively, connection may be made via a fused double
pole isolator having a contact seperation of 3mm in all poles
and serving the appliance and system controls only.
TECHNICAL DATA - Page 7
Boiler Type B11Bs
Maximum Working Head 30.5m (l00ft)
Minimum Working Head (Fully pumped systems) 150mm (6in)
Minimum Circulating Head (Gravity systems) 1.2m (4ft)
Gas Supply Pressure 20 mbar
Maximum Flow Temperature 82°C
Electricity Supply 240v ~ 50Hz fused at 3A
Flow/Return Connection 28mm copper
Gas Supply Connection Rc, ½ (½ in BSP Female)
Power Consumption 20 watts
30 & 40 model 50 & 60 model
Water Content 1.8 litre 2.5 litre
0.4 gal 0.55 gal
Appliance Weight - installed 36.3 kg 44.0kg
80.0 lbs 97.0 lbs
Appliance Weight - lift 31.0kg 38.5 kg
BOILER INJECTOR GAS RATE INPUT OUTPUT BURNER PRESSURE
SIZE SIZE m3/h (ft3/h) Kw(Btu/h) kW(Btu/h) Mbar in wg
Min 0.76 (26.84) 8.20 (27978) 5.86 (20,000) 7.8 3.1
30 2.6mm 0.95 (33.54) 10.18 (34734) 7.33 (25,000) 11.8 4.7
Max 1.09 (38.49) 11.72 (40000) 8.79 (30,000) 15.7 6.3
Min 1.15 (40.51) 12.29 (41930) 8.79 (30,000) 9.5 3.8
40 3.1mm 1.33 (46.98) 14.25 (48620) 10.26 (35,000) 12.7 5.1
Max 1.46 (51.49) 15.62 (53295) 11.72 (40,000) 15.3 6.1
Min 1.47 (51.90) 15.74 (53700) 11.72 (40,000) 9.3 3.8
50 3.55mm 1.65 (58.36) 17.70 (60400) 13.19 (45,000) 11.6 4.7
Max 1.81 (64.00) 19.41 (66225) 14.7 (50,000) 14.2 5.7
Min 1.86 (65.68) 19.9 (68000) 14.7 (50,000) 10.8 4.3
60 3.8mm 2.01 (70.97) 21.60 (73800) 16.12 (55,000) 13.0 5.2
Max 2.17 (76.62) 23.3 (79500) 17.6 (60,000) 15.2 6.1

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TECHNICAL DATA - Page 8
Circulation Pump Selection
The resistance through the heat exchangers when operating
with a water flow rate producing an 11°C temperature rise at
maximum boiler output is shown in TABLE 2. If other
controls, such as three-position valves are used in the
system, the resistance through them, quoted in their
manufacturers literature must be taken into account. The
pump may be fitted on either the flow or return and on
FULLY PUMPED systems MUST be wired directly to the
boiler terminal block, see Fig 14.It must be fitted with two
isolating valves which are positioned as close to the pump
as possible. Isolation of the valves must always leave the
open vent unobstructed.
TABLE 2

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TECHNICAL DATA - Page 9
THE SYSTEM
The boiler must be used on INDIRECT hot water systems
only. It is suitable for use on open vented gravity hot
water/pumped central heating systems or fully pumped
systems which may be sealed or open vented
The system should be designed so that the maximum static
head does not exceed 30.5m (l00ft) and a minimum on fully
pumped systems of 150mm (6in). See Fig 4.
Gravity domestic hot water circuits should have a minimum
circulating head of 1.2m (4ft). See Fig 5. Excessive
horizontal runs should be avoided, but if this is not possible
the circulating head should be increased.
If the boiler is to be used on a system with gravity hot water
the bulb of the overheat thermostat should be repositioned
as shown on Fig 2.
To prevent reverse circulation in the gravity circuit when the
pump is running an injector disc is provided to form an
injector tee at the return connection on the boiler. See
Fig 11.
To prevent nuisance operation of the overheat thermostat, it
is important that where electrically operated zone valves are
used the boiler is wired so that it does not cycle when the
zone valves are closed. Also systems fitted with controls that
close both hot water and central heating circuits while the
boiler is still hot must be fitted with a by-pass circuit to
dissipate the residual heat within the boiler.
Further information on by-pass arrangements is provided in
later notes and illustrations.
Drain-off taps should be fitted in the pipework close to the
boiler and in low points in the system.
NOTE
Although the system can be emptied using the drain-off taps
in the pipework around the system, to empty the boiler it is
necessary to remove the drain-off plug situated in the return
header at the lower right-hand side of the casting. See Fig 2.
COMBINED GRAVITY HOT WATER AND PUMPED
CENTRAL HEATING SYSTEMS
Where a cylinder thermostat and zone valve are fitted to
control the temperature of the domestic hot water it is
recommended that a by-pass be installed
in the gravity circuit. A suggested method of doing this is
shown in Fig 5 where the bathroom radiator is connected
into the gravity circuit and is fitted with two lockshield valves.
Mechanically operated thermostatic domestic hot water
temperature control valves which allow the boiler to operate
when the valve is closed MUST NOT BE FITTED.
FULLY PUMPED SYSTEMS
The pump must always be wired directly to the boiler
terminal block as shown in Fig 13.
If a three port diverter valve is used as shown in Fig 4 a by-
pass is not necessary since one circuit is always open.
Where a pair of two port valves are used, a by-pass is
necessary. The total length of the by-pass circuit taken from
the boiler connections should be greater than 4 metres of
22mm pipe. It should be fitted with a lockshield valve and
adjusted to maintain a minimum flow through the boiler of
4.5 litres/min (1 gal/mm), see Figs 4& 6.
Systems fitted with controls which allow the boiler to operate
when both the hot water and central heating circuits are
closed (i.e. mechanically operated thermostatic control
valves) must be fitted with a by-pass circuit capable of:-
1. Dissipating a minimum of 1 kw (3400 Btu/h).
2. Maintaining a minimum water flow through the boiler of 9
litres/min (2 gal/min).
A suggested method of meeting these requirements by using
a bathroom radiator fitted with two Iockshield valves is
shown in FIGS. 4,6.
Additional system information can be found in the Control
Systems, Pipework and wiring guide.
SEALED SYSTEMS (FULLY PUMPED)
The installation must comply with the requirements of
BS6798 and BS5449 Part 1. The ‘British Gas publication
British Gas Specification for Domestic Wet Central Heating
Systems’ should also be consulted.
Safety Valve
A non-adjustable spring-loaded valve, pre-set to operate at
3bar (45lbf/in2) shall be used. It must comply with BS6759
Part 1 and include a manual

10
TECHNICAL DATA - Page 10
testing device. It shall be positioned in the flow pipe either
horizontally or vertically upwards and close to the boiler. No
shut-off valves are to be placed between the boiler and
safety valve. The valve shall be installed into a discharge
pipe which permits the safe discharge of steam and hot
water such that no hazard to persons or damage to electrical
components is caused.
Pressure Gauge
A pressure gauge incorporating a fill pressure indicator,
covering the range 1-4bar (60lbf/in2) shall be fitted to the
system. It should be connected to the system, preferably at
the same point as the expansion vessel. Its location should
be visible from the filling point.
Expansion Vessel
A diaphragm-type expansion vessel to BS4814 Part 1 shall
be fitted close to the inlet side of the pump. The connecting
pipework should not be less than 15mm (½ in nominal).
Pipework connecting the expansion vessel should not
incorporate valves of any sort. Methods of supporting the
vessel are supplied by the manufacturer. The nitrogen or air
charge pressure of the expansion vessel shall not be less
than the hydrostatic head, (height of the top of the system
above the expansion vessel). To size the expansion vessel it
is first necessary to calculate the volume of water in the
system in litres. The following volumes may be used as a
conservative guide to calculating the system volume.
Boiler Heat Exchanger 6.5 litres
Small Bore Pipework 1 litre per kW of
system output
Micro Bore Pipework 7 litres
Steel Panel Radiators 8 litres per kW of
system output
Low Water Capacity
Radiators 2 litres per kW of
system output
Hot Water Cylinder 2 litres
If the system is extended, the expansion vessel may have to
be increased unless previous provision has been made for
the extension. Where a vessel of the calculated size is not
available, the next available larger size should be used.
The boiler flow temperature is controlled at approximately
82°C.
The vessel size can now be determined from the following
table where V = System volume in litres.
Vessel Charge 0.5 .0
Pressure (bar)
Initial System
Pressure (bar) 0.5 1.0
Expansion Vessel
Volume (litres) V x 0.833 V x 0.11
This is a general guide; if it is required to be more accurate
refer to BS7074.
Cylinder
The hot water cylinder must be an indirect coil type or a
direct cylinder fitted with an immersion calorifier suitable for
operating at a pressure of 0.3bar (5lbf/in2) in excess of
safety valve setting. Single feed indirect cylinders are not
suitable for sealed systems.
Method of Make-Up
Provision shall be made for replacing water loss from the
system either:-
i) from a make-up vessel or tank mounted in a position
higher than the top point of the system, and connected
through a non-return valve to the system on the return
side of all heat emitters.
or
ii) Where access to a make-up vessel would be difficult by
using the mains top up method or a remote automatic
pressurisation and make-up unit as illustrated in Fig 6
METHODS 1 & 2.
Mains Connection
There shall be no connection to the mains water supply or to
the water storage tank which supplies domestic water even
through a non-return valve, without the approval of the local
Water Authority.
Filling Point
The system shall be fitted with a filling point at low level
which incorporates a stop valve to BS1010 and a double
check valve (approved by the National Water Council) to be
fitted in this order from the system mains. Refer to Fig 6
METHOD 1.

11
TECHNICAL DATA - Page 11
Figure 4 OPEN VENTED FULLY PUMPED SYSTEM WITH A COMBINED FEED AND VENT
Figure 5 OPEN VENTED GRAVITY DOMESTIC HOT WATER PUMPED CENTRAL HEATING

12
TECHNICAL DATA - Page 12
Figure 6 FULLY PUMPED SEALED SYSTEM

13
INSTALLATION INSTRUCTIONS - Page 13
It is the law that all gas appliances are installed and serviced
by competent persons as stated in the Gas Safety
(Installation and Use) Regulations 1994.
Electrical installation and servicing should be carried out by
a competent person in accordance with the I.E.E. Wiring
Regulations
For Health and Safety information see back page.
The boiler and its associated equipment will arrive on site in
one cardboard carton. The contents of the carton is as
follows:-
Boiler
Template
Boiler Mounting Plate
Literature Pack containing:
Installation & Servicing Instructions
Users Instructions
Control System Pipework and Wiring Guide
Auxilliary Pack containing
Gas Service Cock
Accessory Packs
Adjustment screws
Figure 7 TEMPLATE
Place template in proposed boiler position taking due
account of the information given previously and the position
of the flue, (the minimum side clearances are automatically
allowed for). Refer to page 5 for top and bottom clearances
which can be measured from the template. Ensure that the
template is level and mark hole positions ‘B’.
If the flue is to rise through the ceiling, mark out centre line
of hole for flue by extending the dotted line on template
vertically and measure out 158mm from rear wall as
illustrated.
Figure 8 SECURING BOILER
MOUNTING PLATE
Remove template and drill holes ‘B’ to a depth of 50mm
using a 7mm drill. Cut hole through wall or ceiling as
necessary for intended run of flue pipe.
Using wall plugs, screws and washers (accessory pack A)
attach boiler mounting wall plate to wall ensuring that it is
level.

14
INSTALLATION INSTRUCTIONS - Page 14
Figure 9 PREPARING BOILER
The controls cover should have been removed when
unpacking the boiler, if not pull controls cover forward 25mm,
lower to release from the four side fixings and pull forward
clear of the thermostat knob
Remove door by undoing the two lower fixing screws and lift
door off the two upper hinge brackets.
Engage adjustment screws into the boiler legs but do not
screw in fully at this stage

15
INSTALLATION INSTRUCTIONS - Page 15
Figure 10 LIFTING AND ALIGNING BOILER
Lift boiler onto the mounting bracket and adjust the boiler
position to obtain a minimum of 5mm clearance from any
side wall or cupboard.
Secure boiler to the mounting bracket using 5mm screw from
accessory pack A.
Undo the screws securing the transportation feet. Discard
feet and screws.
Correct vertical alignment with rear wall as necessary using
the adjustment screws
Remove the temporary cardboard packing pieces from either
side of the casing
Remove the four securing screws and withdraw the inner
draught diverter assembly. Check that the flueway baffles
are correctly located and retained in the flueways as shown
in Fig 10. Reassemble the draught diverter.
Make the flue connection to the boiler draught diverter
sealing the joint with a suitable compound. Refer to the
notes under FLUE page 6.
The weight of the flue must be supported independently
NOT by the boiler.

16
INSTALLATION INSTRUCTIONS - Page 16
Figure 11 PIPE CONNECTIONS
Connect the system pipework to the boiler, compression
fittings are recommended. If however, capillary fittings are
used, it is essential to temporarily remove the thermostat
bulb from the flow pipe before soldering.
A drain off tap should be installed close to the boiler if it is in
a low point of the system.
On combined gravity hot water/pumped central heating
installations the flow and return pipes for both the gravity hot
water circuit and pumped central heating circuits must be
connected to tees fitted directly to the flow and return pipes
on the boiler.
The gravity circuit should be installed in 28mm copper pipe.
28mm tees should be used.
The injector disc (accessory pack G) must be positioned in
the pumped return branch of the tee as illustrated in Figs 11
& 11B.
Remove gas service cock from the auxilliary pack and attach
it to the union nut on the inlet to the gas assembly.
With the inlet connection of the gas service cock facing the
rear, connect the gas supply pipe.
Figure 11B WARNING: UNDER NO
CIRCUMSTANCES SHOULD A
‘REDUCING SET’ BE FITTED
Figure 12
NOTE
The boiler is despatched with the overheat
Thermostat bulb positioned for FULLY PUMPED OPEN
VENTED OR SEALED SYSTEMS.
ONLY if the boiler is to be used on a GRAVITY DHW system
should the bulb of the overheat thermostat be repositioned
as described below, to prevent nuisance operation of the
overheat thermostat.
Remove clip securing overheat thermostat bulb to the flow
pipe.
Uncoil the thermostat capillary and route it through the two
retaining clips attached to the front flange on the top panel.
Position the thermostat bulb in the indent in the return pipe
and secure in this position using the clip previously removed.

17
INSTALLATION INSTRUCTIONS - Page 17
Figure 13 PRINCIPAL OF WIRING
WIRING
WARNING: This appliance must be earthed.
The boiler and all external control circuit wiring must be
supplied from the same single isolating switch and should be
fused at 3A.
Care must be taken to ensure that all wiring to the boiler is
kept clear of sharp edges and hot surfaces.
Ensure that the earth conductor is longer than the L, N, and
SWL from the point of anchorage, so that the current
carrying conductors become taut before the earth conductor,
if the cable is pulled out of the cable clamp.
The boiler terminal block which is situated in the control box
is not designed to accept wiring from all the on site controls
and therefore the installer will usually need to incorporate a
suitable junction box or Potterton Electronic Programmer.
The principle of wiring is shown in Fig 13. It should be noted
that the pump must be wired directly to the boiler terminal
block on FULLY PUMPED systems and to the junction box
or programmer on combined GRAVITY HOT
WATER/PUMPED CENTRAL HEATING systems.
Figure 14 ACCESS TO THE BOILER
ELECTRICAL TERMINAL BLOCK
Remove control box securing screw and lower the control
box to gain access to the boiler terminal block.
Figure 15 WIRING THE BOILER
FOR A FULLY PUMPED SYSTEM
Route a four core cable through the plastic bush at the rear
of the control box and the cable clamp as illustrated Fig 15,
and connect it to the boiler input terminals as follows:-
Permanent live to terminal marked MAINS ‘L’
Neutral to terminal marked MAINS ‘N’
Earth to terminal marked MAINS +
Switched live from external controls to terminal marked
MAINS SwL.
If there are no secondary controls fitted connect the SwL
terminal to permanent live in the external junction box.
Secure the cable within the cable clamp by tightening the
securing screws.
Following the pump manufacturers instructions connect the
pump supply wires to terminals marked PUMP, L, N and 4”
on the boiler terminal block.
Route the cable through the plastic bush in the rear of the
control box and cable clamp as illustrated Fig 15. Secure
cable in cable clamp by tightening the two securing screws.
Close control box and replace securing screw.

18
INSTALLATION INSTRUCTIONS - Page 18
Figure 16 WIRING THE BOILER FOR
COMBINED GRAVITY HOTWATER/PUMPED
CENTRAL HEATING SYSTEM
Route a three core cable through the plastic bush in the rear
of the control box and the cable clamp as illustrated I Fig 16.
Connect the cable to the boiler input terminals as follows:
Switched live on the GRAVITY DHW control circuit to
terminal marked MAINS ‘SwL’
Neutral to terminal marked MAINS ‘N’
Earth to terminal marked MAINS
Secure the cable within the clamp by tightening the two
securing screws.
The pump should be connected to PUMPED CENTRAL
HEATING control circuit at the junction box. See FIG. 13
Figure 17 FUNCTIONAL FLOW DIAGRAM
Figure 18 BOILER WIRING DIAGRAM

19
COMMISSIONING - Page 19
Open Vented Systems
Remove the pump and flush out the system thoroughly with
cold water. Refit the pump, fill and vent the system and
examine for leaks.
Sealed Systems
The system can be filled using a sealed system filler pump
with a break tank or by any other method approved by the
local Water Authority. Refer to FIG 6 and BS6798 1987.
Remove pump and flush out the system thoroughly with cold
water. Re-fit the pump. Fill and vent the system until the
pressure gauge registers 1.5 bar (22.5lbf/in2), examine for
leaks. Raise the pressure until the safety valve lifts. This
should occur within ± 0.3 bar of the pre-set lift pressure of 3
bar. Release water to attain the correct cold fill pressure.
All Systems
The whole of the gas installation including the meter should
be inspected and tested for soundness and purged in
accordance with the recommendations of BS6891.
Fit the case door into position by lifting it onto the top hinge
brackets and secure it with the lower two fixing screws.
First Lighting
A. Ensure that the pump and radiator isolating valves are
open.
B. Turn the boiler thermostat to the ‘0’ position.
C. Turn on the main gas supply and the gas service cock
on boiler.
D. Ensure that the time control, if fitted is in an ‘ON’
condition, and that the room and/or cylinder thermostats,
where fitted are set to high temperatures.
E. Switch on the external electricity supply to the boiler. In
the event of an electrical fault after installation of the
appliance, preliminary electrical system checks must be
carried out as described in the BG multimeter instruction
book. The checks to be carried out are:
A - Earth Continuity, B - Short Circuit, C - Polarity, D -
Resistance to Earth.
F. Partly depress and turn the gas control knob clockwise
ensuring the symbol •lines up with the datum mark on
the gas valve body. See Fig 19. This ensures that the
valve is in the ‘OFF’ condition.
G. Partly depress and turn the control knob anti-clockwise
until the symbol * lines up with the datum mark on the
gas valve body. Press and hold in the control knob and
press the spark generator button until a click is heard.
Release the spark generator button and repeat
operation until the pilot ignites. See Figs 2&19. Hold in
the control knob for a further 15 seconds. On release the
pilot should remain alight. Partly depress and turn the
control knob anti-clockwise until the symbol lines up with
the datum mark on the gas valve body.
NOTE:
On first lighting, establishment of the pilot flame may be
slightly delayed due to the presence of air in the pipework. If
the pilot fails to light or goes out at any time, immediately
turn the control knob clockwise as far as possible, then
release it and wait three minutes before repeating the
lighting procedure. The control knob should not be touched
during this period.
H. Turn the boiler thermostat on and to a high setting and
the main burner will light.
I. Set the boiler thermostat and the room and/or cylinder
thermostat(s) and time control, where fitted, to their
required operating conditions.
J. After the boiler has operated for five minutes check that
there is no spillage or leakage of combustion products in
accordance with BS5440 Part 1. Check soundness of all
appliance gas carrying components and joints using leak
detection fluid and a mirror where necessary.
K. Switch off the boiler, using the thermostat knob.
NOTE: If the main burner fails to light turn the boiler
thermostat to the off position and check that the spillage
detector thermostat reset button (see Fig 18a) is pressed in,
then repeat operation. If you have to keep resetting the
thermostat, or the main burner fails to light consult the fault
finding chart on page 26, Fig 23.
Figure 18a

20
COMMISSIONING - Page 20
FINAL ADJUSTMENT
A. Remove the screw from the burner pressure test nipple
on the gas control valve and fit a pressure gauge to the
test nipple. See Fig 19.
B. Turn on the boiler thermostat, then check that the
pressure is in accordance with the values stated under
TECHNICAL DATA. The burner pressure is factory set
to the maximum stated.
C. If burner pressure adjustment is necessary, remove the
screwed cap from the gas control valve, see Fig 19, and
turn the screw beneath clockwise to increase pressure
and anti-clockwise to reduce pressure.
D. With the burner set to its correct pressure, the firing rate
given in TECHNICAL DATA should also be obtained
and this should be checked by meter reading 10 minutes
after the main burner has been lit.
E. Shut down the boiler, remove the pressure gauge.
Replace the screwed cap and refit the screw in the test
nipple. Re-light and test for gas soundness at the test
nipple screw.
F. Remove the self-adhesive arrow from the inspection
ticket tied to the burner supply pipe and stick it to the
Data Plate inside the controls cover to indicate the
appropriate burner setting pressure. Refit the controls
cover.
G. Heat the system to maximum. Check for water leaks,
turn the boiler off, drain the system whilst hot.
H. Refill the system and on sealed systems adjust to the
correct cold fill pressure. Set the pressure gauge pointer
to the system design pressure.
I. If a by-pass circuit is fitted, the by-pass valve should be
adjusted with the boiler operating under minimum load
conditions to maintain sufficient water flow through the
boiler to ensure that the overheat thermostat does not
operate under normal operating conditions.
J. Remove the temporary label from the front of the casing,
having checked compliance with the information it
contains
Figure 19 GAS CONTROL VALVE Figure 20 PILOT BURNER
Pilot Burner
The pilot burner pressure is non-adjustable. The pilot flame
should heat the thermocouple so that the pilot safety device
is “held in” but must not cause the thermocouple to glow
bright red. Fig 20 illustrates the approximate size of a correct
flame. The E.M.F. generated by the thermocouple should be
of the order of 20-30 mV open circuit, 10-14 mV closed
circuit. Due to the voltage drop in the overheat thermostat
circuit there should be 6.5-8.5 mV closed circuit at the
connection to the gas control valve. Drop out should occur
between 1-3 mV closed circuit. If these conditions cannot be
achieved check that the inlet pressure is 20 mbar See Fig 19
for inlet pressure nipple. If this is correct contact Potterton
Myson.
Boiler Thermostat
At its minimum and maximum settings, the thermostat
should control the water flow temperature at approximately
55ºC-82ºC (130ºF -180ºF). The thermostat has been
calibrated by the makers and no attempt should be made to
re-calibrate it on site. Turn the thermostat to the ‘O’ position
and check that the main burner shuts down.
Pump Over-run Thermostat (Applicable on fully pumped
systems only)
The over-run thermostat will keep the pump running when
the boiler has shut down, as long as the combustion
chamber is hot.