Potterton Mersey Super Quick guide

INSTALLATION AND SERVICE INSTRUCTIONS
Mersey Super
Gas Fired Water Heater
MY99001A
G.C. NO.52476 38
NON SPOUTED MULTIPOINT MODEL FOR USE WITH NATURAL GAS
THE GAS SAFETY (INSTALLATION AND USE) REGULATIONS 1984.
“In your own interest, and that of safety, it is law that all gas appliances are installed by competent persons, in accordance
with the above regulations. Failure to install appliances correctly could lead to prosecution.”
Installation must be in accordance with the Building Regulations, Byelaws of the Water Undertaking, and I.E.E. Wiring
Regulations. It should be in accordance also with any relevant requirements of the Local Gas Region and Local Authority
and the relevant recommendations of the following British Standard Codes of practice: BS 6891, BS 5440:1:2 and BS 5546.
LEAVE THESE INSTRUCTIONS WITH THE USER FOR USE ON FUTURE CALLS
IMPORTANT
PLEASE READ THIS BOOK
BEFORE INSTALLING,
OPERATING OR
SERVICING THIS
APPLIANCE.

1. INTRODUCTION - Page 2
The Main Mersey Super is a room sealed instantaneous water heater designed to supply hot water to several outlets which
may be situated in different rooms, but not necessarily at the same time.
The pilot is lit by a piezo spark igniter: no batteries or electricity are required. The main burners will automatically light when
a domestic hot water tap is turned on and go out when the tap is turned off.
This appliance is not suitable for use with a swivel spout.
ENERGY CUT-OFF DEVICE
This appliance contains an Energy Cut-Off Device that will shut down the gas supply to the appliance if the water within
the heat exchanger exceeds the anticipated temperature limit after the hot water tap has been turned off - See Page 21.
VENTILATION
Being a room sealed appliance, the Mersey Super does not require an air vent in the room or space in which it is installed.
Where this appliance is installed in a compartment, air vents to the compartment at both high and low levels, should be
provided for cooling.
Further guidance is given in BS 5440 Pt.2.
Position of Air Vent
High Low
In compartment which is ventilated to room 274 cm² 274 cm²
42 in² 42 in²
In compartment which is ventilated to outside 137 cm² 137 cm²
21 in² 21 in²
GENERAL
IMPORTANT: The area of wall covered by the appliance must be flat.
The clearances required around the Flue Terminal are shown on the Flue Template supplied with the Terminal Pack.
The appliance must be fitted on an external wall to allow the Flue Terminal to pass directly through the wall to the outside
air.
If the appliance is to be installed into a “SEDUCT” the minimum duct required is 228mm (9in.) deep, 349mm (1 5½in.) wide.
This appliance may take the place of an existing appliance and will mount onto the original flue terminal of any of the
following: AVON, BRISTOL, MEDINA, MEDINA D/L, MEDWAY, MERSEY, SEVERN 3, SEVERN 4, SEVERN 5 and TRENT.

2. TECHNICAL SPECIFICATIONS - Page 3
Finish White stoved paint with contrasting chassis
Weight Packed 21.0 kg. (46.2 lb.)
Weight without Water 17.8 kg. (39.2 lb.)
Weight with Water 18.6 kg. (41.0 lb.)
Water Capacity 0.75 litre (0.17 gall.)
Input 30.3 kW (103,000 Btu/h.)
Maximum Output 22.7 kW (77,400 Btu/h.)
Flow Rates 6.5 1/mm at 500C rise
Minimum pressure head requirement at water heater * 1 bar (14.6 psi) under flow conditions
Maximum pressure head 13 bar (189 psi)
Gas group G 20
Burner injector (140ff) 1.2mm marking 120
Pilot injector 0.27mm marking A
Nominal burner pressure ** (maximum input) 12.5 mbar (5 in. w.g.)
Connections - Gas
- Water 15mm Copper Tail 15mm Compression
Balanced flues (telescopic) Wall thickness available 100mm - 150mm (4in - 6in) - Part No 31/1 0321
150mm - 230mm (6in - 9in) - Part No 31/1 0322
230mm - 380mm (9in - 15in) - Part No 31/1 0323
380mm - 610mm (15in - 24in) - Part No 31/1 0324
Flue Terminal Guard (Optional) Part No 10/1 0262
Notes:
*Additional external pipework and fittings may affect the resistance and must be taken into account on installation.
** The nominal burner pressure should be 12.5 mbar and will only be obtained if the appliance inlet pressure is correct at
20 mbar even when the appliance is running at full heat input. The meter should be capable of passing 1 00ft3/h of
natural gas plus the requirements of any other gas appliances.
MINIMUM CLEARANCES
Above 60mm
Below 75mm
Sides 5mm (Each)
Front 220mm (To allow for removal of outer case)
For ease of servicing, allow as much clearance as possible below the appliance.
If the appliance is to be installed in a cupboard, the ventilation openings in the cupboard must NOT be blocked. DO NOT
USE THE CUPBOARD FOR STORAGE.
Identification
Badge
Data Badge
420mm
265mm
762mm
Overall
Dimensions
Fig. 1

3. INSTALLATION - Page 4
MY99003A
Flue
Terminal
Keep
(4 - Stud Terminal Shown)
Fig. 2
A. LOCATION
1. If the appliance is to be fixed to a suitable existing
terminal first isolate and remove the old appliance.
Leave the flue terminal in place. Retain the fixing nuts
and washers. Make good any damage to the brickwork
or plaster around the terminal. Cut off the existing
pipework at a convenient point below the appliance.
2. If installing a new flue terminal, guidance is given on
the template sheet supplied with the terminal pack.
NOTE: Where the appliance is to be installed into a
SEDUCT the minimum duct required is 228mm (9in) deep,
349mm (15½ in) wide.
Outer Case
Bottom Cover
Bag Of
Accesories
Fig. 3
3. Where the building regulations require it, a flue terminal
guard should be fitted symmetrically around the outer
part of the flue terminal.
4. Unpack the water heater. Find the bags of accessories
before discarding the packaging.
5. Slide off the bottom cover then remove the three
screws securing the outer case and carefully lift it off.
Terminals
With 2 StudsTerminals With 4 Studs
Cover
Cover
Fig. 4
6. Use the self adhesive discs supplied to cover the
unwanted fixing holes in the back of the new appliance
as shown.

INSTALLATION - Page 5
7. Fit the flue terminal sealing strip (packed separately in
the carton) into the recess around the flue aperture in
the back of the appliance.
8. Lift the appliance into position, locating the flue outlet
into the circular duct on the flue terminal.
9. Secure with the appropriate nuts and washers.
Fig. 5
B. GAS CONNECTION
IMPORTANT: Blow out all foreign matter from the supply
pipe before connecting to the gas service cock.
15mm copper pipe to BS 2871 may be used for a simple
supply not exceeding 3 metres (10ft) from the gas meter.
Where the installation contains many bends or the length is
in excess of 3 metres (l0ft), then the use of 22mm copper
pipe is necessary.
1. Assemble the filter, ‘O’ ring and inlet tail to the gas inlet.
2. Depending on whether the main supply pipe is to be
routed vertically or horizontally to the appliance,
connect the gas service cock (stamped ‘G) either
directly to the gas inlet tail or within the supply pipe.
NOTE: The service cock should be as close to the
appliance as possible and the ON/OFF screw in an
accessible position.
3. Ensure that the gas supply is turned OFF at the mains.
4. Connect to the gas supply.
5. Turn ON the gas supply and the gas service cock then
test for gas soundness (BS 6891).
IMPORTANT: DO NOT TRY TO LIGHT THE APPLIANCE
AT THIS STAGE. TO ALLOW THE MAIN BURNER TO
IGNITE WITHOUT THE OUTER CASE SECURED IN
POSITION IS A HAZARD.
MY99022A
OFF
Gas Inlet
Gas Filter
'O' Ring
Gas Inlet Tail
Gas Service Cock
On / Off Screw
Fig. 6

INSTALLATION - Page 6
Fig. 7
C. WATER CONNECTIONS
IMPORTANT: Flush out all foreign matter from the supply
pipe before connecting to the service cock.
1. Assemble the filter, olive and inlet tail to the water inlet.
NOTE: The inlet tail need not be used as a vertical
supply can be routed directly onto the water inlet.
2. Depending on whether the main supply pipe is to be
routed vertically or horizontally to the appliance,
connect the water service cock either directly to the
water inlet tail or within the supply pipe. NOTE: The
service cock should be as close to the appliance as
possible and the ON/OFF screw in an accessible
position.
3. Ensure that the mains water supply is turned OFF.
IMPORTANT: When routing the supply pipe to the
appliance, ensure that it can be lowered by approx 25mm to
allow for disconnection when servicing.
4. Connect the hot water supply pipes to the water outlet -
15mm compression.
5. Turn ON the mains water supply, turn ON the water
service cock and open all the hot water outlets to allow
water to flow. Purge the air from the system by closing
the hot water outlets starting with the lowest level and
ending with the outlet at the highest level.
6. Check for water leaks and remedy if found.
IMPORTANT: DO NOT TRY TO LIGHT THE APPLIANCE
AT THIS STAGE.
MY99008A
Filter Guaze
Union Nut
Pilot Tube
Fig. 8
D. LINT FILTER
This appliance has a lint filter fitted around the
base of the pilot tube.
Ensure that the filter gauze is located inside both end caps
and that the complete assembly is correctly seated over the
union nut at the base of the pilot tube.

4. COMMISSIONING - Page 7
WARNING: The outer case of this appliance is not merely a
cosmetic device. It is a functioning component in the air
supply to the burner and MUST BE replaced with great care
NOW, before any attempt is made to light the burners.
TO ALLOW THE MAIN BURNER TO IGNITE WITHOUT
THE CASE IN POSITION IS A HAZARD.
1. Refit the outer case ensuring it is correctly seated then
secure (3 screws).
MS99004A
Outer Case
Fig. 9
2. Ensure that the gas and water supplies are turned ON.
3. Ensure that all hot water outlets are closed.
4. Remove the screw and sealing ring from the burner
pressure test point and attach a pressure gauge.
Fig. 10
5. Fully depress and hold the ON button ‘ ’and
repeatedly press and release the IGN button ‘ ’until
the pilot is lit. The pilot flame can be observed through
the pilot viewing window.
6. Hold the ON button ‘ ’in for a further 10 seconds after
the pilot is lit, then release. If the pilot goes out, repeat
the lighting operation keeping the ON button
‘‘depressed a little longer.
7. Test for gas soundness using a suitable leak detection
fluid on all external gas joints.
8. Open a hot water outlet and the burner will ignite. Allow
the water to run for a few minutes then check the
burner pressure - it should be 12.5 mbar (5 in w.g.), if
the pressure is not correct see the FAULT FINDING
section.
Fig. 11

COMMISSIONING - Page 8
Fig. 12
NOTE: If a gas rate check is required, the gas consumption
after 3 minutes running should be approximately
48.5 l/mm (1.7³/min).
9. Turn OFF the hot water outlet and press the OFF button
’‘ on the appliance. Remove the pressure gauge
and replace the screw and sealing ring.
10. Relight the pilot. Turn ON a hot water outlet and check
for gas soundness at the pressure test point.
11. Turn OFF the hot water outlet. Slide the bottom cover
onto the appliance.
Fig. 13
Explain to the user how to operate the appliance.
- see the “Instructions for Use” booklet.
Show the user the position of the Identification Badge.
HAND OVER THE “INSTRUCTIONS FOR USE” TO THE
USER.
LEAVE THESE “INSTALLATION AND SERVICE”
INSTRUCTIONS WITH THE USER FOR USE ON FUTURE
CALLS.
ADVISE THE USER THAT FOR CONTINUED EFFICIENT
AND SAFE OPERATION OF THE APPLIANCE, IT IS
IMPORTANT THAT SERVICING IS CARRIED OUT AT
INTERVALS RECOMMENDED BY THE LOCAL BRITISH
GAS REGION OR C.O.R.G.I. REGISTERED INSTALLER.
5. SERVICING - Page 8
To ensure continued efficient operation of the appliance, it is recommended that it is checked and serviced as necessary at
regular intervals. The frequency of servicing will depend upon the particular installation conditions and usage, but in general
once per year should be adequate.
IMPORTANT: It is the law that any service work must be carried out by competent persons such as British Gas or other
c.o.r.g.i. registered personnel.
NOTE: In hard water areas, scale may build up on the push rod ,seals and on the underside of the diaphragm housing.
They may require regular descaling and regreasing.

SERVICING - Page 9
Operate the appliance noting any faults in the component
units. Carry out the servicing procedure then correct any
other faults by reference to ‘Replacement of Parts’, in which
section you will find details of how to dismantle and
reassemble the following detailed components. Check that
the burner ignition is smooth and quiet when a hot tap is
opened. The burner ignition has been factory set and should
not need adjustment. However, if adjustment is required a
slow ignition screw is fitted to the appliance and is situated
above the cap screw in the water governor body (fig. 16).
The screw is factory set 2 full turns out (anti-clockwise) from
the fully in position. Turning the screw clockwise delays the
ignition, anti-clockwise advances the ignition.
WARNING: NEVER OPERATE THIS APPLIANCE WITH
THE OUTER CASE REMOVED.
MS99016A
Push Rod and Seal
Pilot Injector
Burner
Assembly
Thermocouple
Fig. 14
1. Check the piezo unit, flame safety device and
thermocouple, clean or replace if necessary.
2. Remove the burner assembly and clean using a soft
brush or vacuum cleaner.
3. Check the pilot injector and clean or replace if
necessary. Also clean the lint filter.
4. Remove the water governor assembly complete with
push rod. Replace the seals if necessary. Descale and
regrease the push rod, washers and diaphragm
housing using Dow Corning 111 silicone grease.
5. Check for water and gas soundness. Replace ‘O’ rings,
sealing washers and gaskets where required.
Water Governor
Flame Safety
Device
MS99005A
Fig. 15
6. Clean any deposits off the heating unit by washing or
brushing. Descale the heating unit if required.
Fig. 16

6. REPLACEMENT OF PARTS - Page 10
IMPORTANT: THE FOLLOWING WORK SHOULD ONLY BE CARRIED OUT BY A COMPETENT SERVICE
ENGINEER. E.G. BRITISH GAS OR CORGI REGISTERED PERSONNEL
1. IF WATER IS DRAINED FROM THE SYSTEM DURING SERVICING, TURN ON ALL HOT TAPS TO PURGE AIR
FROM THE WATER SYSTEM. TURN THEM OFF IN SEQUENCE, STARTING WITH THE TAP AT THE LOWEST
LEVEL.
2. WHEN REPLACING ANY PARTS, RE-ASSEMBLE IN REVERSE ORDER UNLESS OTHERWISE STATED.
This chart shows the steps to be taken in order access a specific part or perform a particular function. Use this chart in
conjunction with the detailed procedures on the following pages.
START
General Access/Main Burner
Remove Piezo Unit
Remove Pilot Injector
Remove Thermocouple and
Electrode
Remove Pilot Injector
Remove Water Governor and
Push Rod
Remove Energy Cut-Off Device
Drain the Appliance
Descale and Regrease
Remove Heating Unit
Remove Flame Failure Device
Remove Water Govenor
Venturi
Descale Heating Unit
Remove the Automatic Valve &
Burner Manifold Complete

REPLACEMENT OF PARTS - Page 11
6.1. PIEZO UNIT
It will NOT be necessary to remove the outer case.
a. Slide out the bottom cover.
b. Disengage the electrode lead from the piezo unit.
c. Remove or loosen and pull aside the spark button
retainer, taking care not to lose the shakeproof washer.
d. Pull off the button and unscrew (anti-clockwise) the
piezo from its housing
MY9909A
Button
Piezo Unit
Electrode
Lead
Spark Button
RetainerShakeproof
Washer
Fig. 17
6.2. GENERAL ACCESS/MAIN BURNER
a. Turn OFF the gas and water supplies at the service
cocks.
b. Slide out the bottom cover.
c. Remove the 3 fixing screws and pull off the outer case.
Fig. 18
d. Remove 4 fixing screws from the burner assembly (2
each side).
e. Remove 2 screws securing the front to the heating unit.
f. Pull the burner assembly slightly forwards to clear the
injectors, then pull apart and withdraw taking care not
to snag the pilot assembly.
NOTE: If required, the burner assembly can be dismantled
and the burner bars replaced individually. On re-assembly
ensure that the burner inlets locate in the 14 holes.
NOTE: On re-assembly of the burner assembly take care not
to snag the pilot assembly. Ensure the front face of the
assembly has located on the two studs on the heating unit.
MY99033A
Screws 2 Off
Screws
Fig. 19

REPLACEMENT OF PARTS - Page 12
Fig. 20
6.3. THERMOCOUPLE AND SPARK ELECTRODE
a. Gain general access - see 6.2.
b. Remove the fixing screw and bracket then lower the
spark electrode.
c. Disconnect the nut securing the thermocouple to the
interrupter at the chassis base.
d. Disconnect the electrode lead from the back of the
piezo unit, pull the lead up through the grommet and
remove.
e. On re-assembly, ensure that the pilot tube bends
towards the rear of the appliance.(The thermocouple
will be vertical and nearest the burner manifold).
Lint Filter
Union Nut
Pilot Tube
Pilot Injector
Pilot Tube
Fig. 21
6.4. PILOT INJECTOR
a. Gain general access - see 6.2.
b. Lift up the lint filter, disconnect the union nut and
carefully lift up the pilot tube taking care not to lose the
pilot injector.
c. On re-assembly ensure the pilot injector is correctly
seated (taper side down) and that the lint filter is
correctly assembled and located on the union nut.
NOTE: The lint filter can be cleaned if required.
Union Nut (Pilot Transfer)
Union Nut
(Supply Pipe)
Screws
(3 Off)
Union Nut
(Gas Connection)
Fig. 22
6.5. FLAME SAFETY DEVICE
a. Gain general access - see 6.2.
b. Disengage the electrode lead from the piezo unit.
c. Release the thermocouple from the back of the flame
safety device.
d. Release the union nuts above and below the flame
safety device.
e. Release the union nut securing the pilot transfer tube to
the flame safety device.
f. Remove the 3 screws securing the flame safety device
to the chassis base and carefully withdraw the unit.
g. Re-assemble in reverse order.

REPLACEMENT OF PARTS - Page 13
h. Test for gas soundness as follows:-
-Ensure the water service cock is in the OFF
position. This will ensure water cannot flow and
open the automatic valve.
-Turn ON the gas, purge and light the pilot, this will
pressurise the burner supply pipe.
-Test the gas supply to flame safety device and
burner supply pipe above the flame safety device for
gas soundness using leak detection fluid.
i. Re-assemble remaining parts and ensure the water
service cock is in the ON position.
Electrode
Thermocouple
Pilot
Fixing Screw
Fig. 23
6.6. TO DRAIN THE APPLIANCE
a. Ensure that the gas and water service cocks are turned
OFF.
b. Open a hot water outlet.
c. Have a suitable container to hand . Remove the drain
screw from the water service cock and allow the water
to drain.
Off
Off
Drain Screw
Water Service Cock
Water Service Cock
Gas Service Cock
On
Off
A
B
D
E
C
Fig. 24
6.7. WATER GOVERNOR
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Release the inlet water connection and lower the
pipework to clear the inlet.
d. Release the union nut and clamping plate then remove
the feed pipe. Replace the ‘O’ ring.
Water Governor
Water Inlet
Connection
Clamping Plate
Union Nut
MS99014A
Fig. 25

REPLACEMENT OF PARTS - Page 14
MS99006A
Screws - 3 Off
Screws - 2 Off
Pressure
Relief
Valve
Fig. 26
e. Remove 2 screws above the chassis base securing the
governor to the automatic valve.
f. Remove 3 screws above the chassis base securing the
governor to the chassis base.
g. Carefully withdraw the governor complete with pressure
relief valve, TAKE CARE NOT TO BEND THE PUSH
ROD. IF THE ROD IS BENT, A NEW ONE MUST BE
FITTED.
h. Remove the push rod.
i. Remove 6 screws and separate the two halves of the
water governor.
Brass Washer
'O' Ring
MY99018A
Fig. 27
DESCALE AND REGREASE
j. Remove both the brass washer and ‘O’ ring from the
top opening. Clean the washer.
k. Clean the top opening then pack with a silicone grease
such as Dow Corning 111.
Fit a new ‘O’ ring and re-fit the brass washer.
I. Hold the thrust plate, remove the fixing nut and lift out
the diaphragm assembly. Clean or renew as required.
On re-assembly, tighten the fixing nut finger tight plus a
¼ turn only.
m. Check and if necessary replace the transfer port ‘O’
ring.
n. Ensure the diaphragm assembly is correctly seated
then re-assemble the two halves of the governor. Insert
the 6 screws and secure finger tight. Fully tighten all 6
screws in the order shown.
o. Clean, regrease and re-fit the push rod or replace with
a new one.
6
1
5
2
3
4
Fig. 28

REPLACEMENT OF PARTS - Page 15
6.8. WATER GOVERNOR VENTURI
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Release the union nut and clamping plate then remove
the feed pipe.
d. Using a large flat bladed screwdriverthat will engage
both slots, remove the venturi.
e. Clean and re-fit.
Fig. 29
6.9. AUTOMATIC VALVE AND BURNER MANIFOLD
COMPLETE
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Remove the water governor - see 6.7.
d. Release the union above the flame safety device. Do
not lose the ‘O’ ring.
e. Release the retaining plate (2 screws) and remove the
burner supply pipe. Do not lose the ‘O’ ring.
f. Prise the manifold location brackets apart and carefully
lift out the complete assembly.
IMPORTANT: The automatic valve and burner manifold
are only available as a combined assembly. Retain all
screws and ‘O’ rings from the old assembly or renew.
NOTE: On re-assembly slide the pressure test point
extension tube through the grommet before locating the
manifold against the location brackets.
MY99020A
Burner Supply Pipe
Union Retaining Plate
'O' Ring
'O' Ring
Fig. 30
g. Re-fit the water governor.
h. Re-connect the burner supply pipe.
i. Test for gas soundness as follows:-
-Ensure the water service cock is in the OFF
position, this will ensure that water CANNOT flow
and open the automatic valve.
-Turn ON the gas, purge and light the pilot, this will
pressurise the burner supply pipe.
-Test the burner supply pipe joints for gas soundness
using leak detection fluid.
j. Re-assemble remaining parts and ensure the water
service cock is in the ON position.
IMPORTANT: If the automatic valve and burner manifold
complete is dismantled, it can only be tested for gas
soundness under pressure AFTER blanking off all the
injectors.
OFF
MY99019A
Drain Screw
Water
Service
Cock
Fig. 31

REPLACEMENT OF PARTS - Page 16
MY99017A
Unions
Heating Unit
Primary Flue
Heat Exchanger
Assembly
Sealing Strip
Fig. 33
6.10. HEATING UNIT
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Remove the 2 screws securing the energy cut-off
device to the heating unit (located top front left).
d. Disconnect the 2 unions.
e. Remove 4 screws securing the unit to the chassis.
f. Carefully pull the unit from the top and lift. DO NOT
lose the ‘0’ rings and washers.
g. Remove the primary flue, secured by 4 screws (2 front,
2 rear).
Acid Resisting
Collector Tank
Heating Unit
Descalent
Or
Hot Water
Pinch Cock
Aci
d
Rubber
Tube
Acid Resisting
Feed Tank
MY99031A
Fig. 33
6.11. DESCALING THE HEATING UNIT
WARNING: ACID/WATER SOLUTION MUST BE USED
WITH EXTREME CAUTION. TAKE CARE NOT TO SPLASH
ONTO SKIN OR INTO THE EYES. WASH ANY AFFECTED
AREAS WITH LARGE AMOUNTS OF COLD WATER AND
SEEK MEDICAL ADVICE.
CARRY OUT THE FOLLOWING OPERATION OUT OF
DOORS. ACID/WATER SOLUTION CAN DAMAGE
FURNISHINGS ETC.
a. Gain general access - see 6.2.
b. Drain the appliance - see 6.6.
c. Remove the heating unit - see 6.10.
d. Invert the heating unit on a suitable bench or table.
e. Using rubber tube and acid resisting tanks, assemble
as shown in fig.33.
f. Fill the upper container with a proprietary brand of
descalent or a solution of 10 parts water to 1 part
hydrochloric acid. The water should preferably be hot,
then add ACID to WATER, not water to acid.
g. Adjust the pinch cock and allow the fluid to slowly pass
through the heating unit into the collecting tank.
h. Continue the process until the fluid ceases to bubble. It
may be necessary to replenish the solution.
i. Disconnect and thoroughly wash out the heating unit
with clean water.

REPLACEMENT OF PARTS - Page 17
6.12. PILOT VIEWING GLASS AND SEAL
a. Complete steps a., b. and c. of section 6.2.
b. The viewing glass and seal are fixed to the inside of the
outer case by 2 metal tabs. Bend back the tabs and
remove the glass and seal. Secure the new glass and
seal to the outer case by bending over the 2 spare
straight tabs.
MY99016A
Tabs
Viewing Glass
Viewing Glass Seal
Fig. 34
6.13. ENERGY CUT-OFF DEVICE
a. Gain general access - see 6.2.
b. Disconnect the energy cut-off leads from the interrupter
located on the underside of the chassis.
c. Remove the 2 screws securing the energy cut-off
device to the heating unit (located top front left).
d. Pull the leads complete with grommets up through the
chassis base.
e. Fit the new energy cut-off device which comes
complete with grommets.
Thermocouple Interrupter
Grommets
View Under Chassis Base
Energy Cut-Off Device
Top Front Left Of Heating Unit
MS9909A
Fig. 35

7. FAULT FINDING - Page 18
SYMPTON POSSIBLE CAUSE SOLUTION
PILOT WILL NOT LIGHT 1. Gas not turned on. 1. Turn on the gas at the gas
service cock and/or the main
gas line.
2. Air in gas line. 2. Purge the air line by depressing
and holding the centre ON
button, this may take 2-3
minutes.
3. Incorrect pilot lighting procedure. 3. Follow the lighting instructions
located on the bottom cover or
refer to the “Instructions for
Use”.
4. Electrode lead not connected to the rear
of the spark igniter. 4. Re-connect the electrode lead.
5. Incorrect spark gap. 5. The gap between the electrode
tip and the pilot hood should be
3-4mm.
6. Current tracking to earth. 6. Check the electrode lead is
routed clear of all metal parts.
7. Pilot injector blocked. 7. Clear injector by blowing
through or replace with pilot
injector Part No 19/12690. Also
clean the lint filter located at the
base of pilot tube.
8. Faulty components. 8. Replace any faulty components
found. Piezo Unit - Part No 10/
11935. Electrode Assembly -
Part No 10/17493.
9. No gas to the appliance. 9. Call in your local British Gas
Region.
PILOT LIGHTS BUT WILL NOT
REMAIN ALIGHT 1. Thermocouple connections loose. 1. Tighten the connections.
2. Pilot flame soft’ or too small to heat the
thermocouple tip. 2. Pilot injector partially blocked, clear by blowing through or
replace. Check the gas inlet
pressure is correct - 20 mbar.
Also clean the lint filter located
at the base of the pilot tube.
3. Thermocouple worn out or damaged. 3. Replace the thermocouple - Part
No 10/17461.
4. Faulty magnet unit in the flame safety
device. 4. Replace flame safety device- Part No 10/13477.
5. Energy cut-off device connections
loose. 5. Tighten connections.
6. Energy cut-off device may be faulty. 6. Check for continuity and replace
if necessary - Part No 10/17792.

FAULT FINDING - Page 19
SYMPTON POSSIBLE CAUSE SOLUTION
PILOT LIT BUT MAIN BURNER
WILL NOT LIGHT ON WATER
FLOW
1. Gas inlet pressure low. 1. Call in your local British Gas
Region
2. Low water flow caused by blocked
water filter. 2. Clean the debris from the filter.
3. Faulty diaphragm. Will also cause a
high water rate 3. Replace the Diaphragm Assembly - Part No 10/17572.
4. Automatic gas valve push rod jammed.
May also cause a high water rate. 4. Dismantle clean and regrease using Dow Corning 111 silicone
grease. Handle the push rod
with care, do not bend.
5. Slow ignition screw incorrectly set. Will
also cause a high water rate. 5. See Fig. 16 for the position of the screw. Turning the screw
clockwise delays the ignition,
anti-clockwise advances the
ignition. The screw should be
set 2 full turns out (anti
clockwise) from the fully in
position. When correct the
burner ignition should be smooth
and quiet when a hot water
outlet is opened.
NO OR LOW WATER FLOW
RATE 1. Blocked water filter. 1. Clean the debris from the filter.
2. Heat exchanger blocked with lime. 2. Descale or replace - Part No
10/17558.
3. Loss of service water main pressure. 3. Contact your Local Water
Authority.
HIGH WATER FLOW RATE See LOW WATER TEMPERATURE
HIGH WATER TEMPERATURE 1. Automatic gas valve push rod sticking.
Water rate will be normal. 1. Dismantle clean and regrease using Dow Corning 111 silicone
grease. Handle the push rod
with care, do not bend.

FAULT FINDING - Page 20
SYMPTOM POSSIBLE CAUSE SOLUTION
LOW WATER TEMPERATURE 1. Gas pressure too low. 1. Check and clean gas filter, also
check gas inlet pressure.
2. Faulty diaphragm. Will also cause a high
water rate. 2. Replace the Diaphragm Assembly - Part No 10/17572.
3. Automatic gas valve push rod sticking.
May also cause a high water rate 3. Dismantle clean and regrease using Dow Corning 111 silicone
grease. Handle the push rod
with care, do not bend.
4. Slow ignition screw incorrectly set. Will
also cause a high water rate. 4. See Fig.16 for the position of the screw. Turning the screw
clockwise delays the ignition,
anti-clockwise advances the
ignition. The screw should be
set 2 full turns out (anti
clockwise) from the fully in
position. When correct the
burner ignition should be smooth
and quiet when a hot water
outlet is opened.
NOISY HEATER 1. Heat exchanger scaled. Ultimately this
will cause the heat exchanger fins to
discolour and buckle.
1. Descale or replace - Part No
10/17558.
2. Noisy ignition could be caused by
incorrect setting of the slow ignition
screw.
2. See Fig. 16 for the position of
the screw. Turning the screw
clockwise delays the ignition,
anti-clockwise advances the
ignition. The screw should be
set 2 full turns out (anti-
clockwise) from the fully in
position. When correct the
burner ignition should be smooth
and quiet when a hot water
outlet is opened.
3. Reduced pilot rate caused by dirt. 3. Clear injector by blowing
through or replace with pilot
injector Part No 19/12690. Also
clean the lint filter located at the
base of pilot tube.
4. Burner aeration ports and main flame
ports blocked. 4. Carefully clean the burners with a vacuum cleaner.