Technical data

19
should NOT have to be forced. If resistance is ex-
perienced, either pipe is not correctly fitted in rear
of water valve or clip is not being fitted properly
through slot between back plate and plastic hous-
ing of water valve. When clip is fitted, check con-
nection by pushing pipe back away from water
valve.
• Refit telescopic connecting pipe to inlet of wa-
ter valve after applying silicone grease to 'O' ring.
Fit retaining clip into groove on connecting pipe,
through slot between back plate and water valve
plastic housing. Check connection by pulling pipe.
Make sure that clip is not loose and likely to fall out
at a later date. If in doubt, fit a new clip.
• Replace microswitch assembly.
• Open isolating valve on cold water inlet connec-
tion and check for leaks.
To replace gas valve
• Ensure gas supply is off.
• Disconnect two black electrical leads from gas
valve modulating coil.
• Disconnect two white and one red lead from gas
valve main solenoid.
• Pull off clear plastic tube from gas valve to sealed
chamber tapping point.
• Unscrew main gas supply pipe nut on top of gas
valve, releasing spark ignition unit bracket, see dia-
gram 27.
• From below boiler, unscrew gas valve connec-
tion between gas valve and isolating cock.
• Unscrew and remove two screws securing gas
valve to bottom plate of boiler.
• Remove gas valve from boiler.
• Refit replacement gas valve in reverse order to
removal.
Note: Use new 'O' ring provided between gas valve
and burner supply pipe.
• Refit electrical connections to replacement gas
valve as follows:
- BLACK leads to modulating coil.
- WHITE leads to EV1 and EV2 terminals of main
solenoid
- RED lead to COM terminal of main solenoid.
To replace modulating coil
• Ensure gas supply is off.
• Disconnect two black electrical leads from gas
valve modulating coil.
• Unscrew and remove two screws holding modu-
lating coil to gas valve and remove coil from gas
valve.
• Fit replacement modulating coil in recerse order
to removal.
• Reconnect electrical leads to replacement coil.
Note: All boilers are tested and factory set during
manufacture. Should it be necessary to reset a gas
valve, for example after replacement, refer to 'Set-
tings'.
To replace safety valve
• Drain down heating circuit of boiler only using
drain point on front of non-return valve (located to
the right of reversing valve.
• Disconnect safety valve discharge pipe from
safety valve.
Diagram 26
Des 058
Diagram 27
Mec 117
• Pull out clips securing safety valve to non-return
valve.
• Remove safety valve from boiler
• Fit replacement safety valve in reverse order to
removal.
Note: Apply silicone grease to 'O' ring before fitting
safety valve into non-return valve body.
• Refill boiler, vent and pressurise as described pre-
viously.
To replace heat exchanger
• Drain down both heating and hot water circuits
of boiler only as described previously.
Note: It is not necessary to drain entire heating sys-
tem to carry out this work.
• Remove combustion chamber cover as de-
scribed in 'Routine Cleaning and Inspection'.
• Remove two clips from heating connections to
left side of heat exchanger.
• Remove clip holding pump outlet connection
into pump and slide connection up pump outlet
pipe. Pull complete pipe down to disengage from
heat exchanger.
• Remove retaining clip from LHS pipe connection
on front section of valve and disengage pipe.
• Disengage pipe downwards from heat ex-
changer.
• Unscrew and disconnect two hot water connec-
tions to right side of heat exchanger.
• Grasp both sides of heat exchanger and slide
forwards and out of boiler.
• Fit replacement heat exchanger in reverse or-
der to removal.
Note: Use new sealing washers and 'O' rings pro-
vided.
• Open isolating valves on flow and return con-
nections, refill, vent and pressurise boiler. Check for
leaks.
SERVICING INSTRUCTIONS