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6. Combustion Chamber Insulation.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 15.3(a).
Remove the inner casing cover, fan, flue hood assembly, burner,
and Gas to Water heat exchanger as described in Sections 14.3
(b, e and f), and 15.4 (5). Remove the fibre insulation pads from
the combustion chamber side, rear, and front sections.
Fit the replacement pads in the reverse order taking care not to
damage them.
Open the valves and fill and re-pressurise the system as
described in Section 12.2.
7. Burner. See Fig. 31.
Check that the electricity and gas supplies to the appliance are
turned off.
Remove the burner assembly as described in Section 14.3 (h).
Fit the replacement burner in the reverse order taking care not to
damage the electrode leads.
8. Burner Injector. See Fig. 31.
Remove the burner as described in Section 14.3 (h).
Unscrew the brass injector from the manifold.
Fit the replacement injector in the reverse order.
9. Spark Electrode Assembly. See Fig. 31a.
Remove the combustion chamber front as described in 14.3 (g)
Carefully pull off the two electrode leads,
Undo the M4 extended nut and remove the spark electrode
assembly from the burner.
Fit the replacement electrode in the reverse order, checking that
the spark gap is 3.5 to 4.5mm.
10. Flame Sensor. See Fig. 31.
Remove the burner as described in sections 14.3(h) and 15.4(8).
Undo the M3 screw and remove the sense electrode from the
burner.
Fit the replacement electrode in the reverse order, checking that
the sense gap is 5 to 6mm.
11. Gas Valve. See Figs. 33. and 34.
Check that the electricity and gas supplies to the appliance are
turned off.
Hinge down the control box assembly in the servicing position
as described in Section 14.3(d).
Whilst supporting the valve unscrew the plug retaining screw
and carefully pull off the electrical solenoid plug connection and
the two modureg leads.
Undo the 8 manifold screws and remove the gas valve. See Fig. 34.
Fit the replacement gas valve in the reverse order ensuring the
“O” rings are correctly fitted.
Turn on the gas supply and check for soundness.
To set the burner pressure. See Fig. 33.
The minimum and maximum burner pressures must be set after
a new gas control has been fitted.
The maximum burner pressure must be set first, as any
adjustment of the maximum pressure influences the minimum
pressure setting.
Start the appliance in the domestic hot water mode as described
in section 12.4. - Appliance Operation.
Adjust the maximum pressure adjustment screw on the gas
valve to give a burner pressure of 13.6 mbar on natural gas, for
propane the maximum pressure adjustment must be increased
to maximum clockwise, this should give 33.0 - 35.0 mbar.
End the demand and reset the appliance by interrupting the
mains electricity supply. (Otherwise there is a four minute anti-
cycle delay at the end of a demand).
Restart the appliance in central heating mode and adjust the
minimum adjustment screw on the gas valve to give a pressure
of 1.0 mbar on natural gas or 3.5 mbar on propane. See Fig. 33.
After completing the adjustments, check the minimum and
maximum pressures and re-adjust as necessary. Once this has
been done the clear cap should be re-fitted to the adjuster and
the retaining screw tightened. Coat the screw with paint or nail
varnish to prevent user adjustment.
12. Central Heating Sensor. See Fig. 34.
Check that the electricity supply to the appliance is turned off.
Hinge the facia assembly in the servicing position as described in
Section 14.3(c and d).
Carefully pull off the two leads from the sensor.
Pull off the sensor and spring retaining clip from the pipe.
Fit the replacement sensor in reverse order with a layer of heat
sink compound between the faces. Refit the leads.
21
Fig. 34. Gas valve pump and air pressure
switch.
Lower pump
connection
Gas valve
electrical
connections
Pressure gauge
connection
Central Heating
Sensor
Air pressure
switch
Air pressure switch
connecting tubes
PumpGas
valve
Top gas valve
connection (4 bolts)
Red
pipe
Fig. 27. Gas valve.
Main gas valve
connections
(Black : blue : brown :
green/yellow)
Burner pressure
test point
Inlet pressure test
point
Electrical connections Ð
modulator (Blue : Blue)
Modulating
solenoid
Minimum
pressure
adjuster
Maximum pressure
adjuster
Note: Clockwise to
increase and anti-
clockwise to
decrease the
pressure
Fig. 31a. Spark electrode assembly.
3.5-4.5mm
2.5-5mm