Open the valves and fill and re-pressurise the system as
described in Section 13.2.
4. Combustion Chamber Insulation.
Refer to Fig. 29.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3, a.
Remove the inner casing cover, combustion chamber, flue
hood assembly, burner, and Gas to Water heat exchanger as
described in Sections 15.3 ,b, e and g, and 16.4 ,3. Remove the
fibre insulation pads from the combustion chamber side, rear,
and front sections. To avoid the risk of fine particles dampen
the pads before removal.
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 13.2.
5. Burner.
Refer to Fig. 27.
Check that the electricity and gas supplies to the appliance are
turned off.
Remove the burner assembly as described in Section 15.3, g.
Fit the replacement burner in the reverse order taking care not to
damage the electrode leads.
6. Burner Injector.
Refer to Fig. 27.
Remove the burner as described in Section 15.3, g.
Unscrew the brass injector from the burner.
Fit the replacement injector in the reverse order.
7. Spark Electrode Assembly.
Refer to Fig. 27.
Remove the combustion chamber front and sides as described in
15.3, f.
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 to 4mm.
8. Flame Sensor.
Refer to Fig. 27.
Remove the burner as described in Sections 15.3, g and 16.4, 5.
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.
9. Gas Valve.
Refer to Fig. 23.
Check that the electricity and gas supplies to the appliance are
turned off.
Hinge down the facia panel into the servicing position as
described in Section 15.3, c.
Remove the air pressure switch bracket as described in
Section 16. 3, 2.
Undo the two G
3
⁄
4
inch nuts on the gas valve and the two M4
screws on the gas valve bracket and withdraw the valve.
Whilst supporting the valve carefully pull off the three electrical
solenoid plug connections.
Fit the replacement gas valve in the reverse order ensuring the
sealing washers are correctly fitted.
Turn on the gas supply and check for soundness.
To set the burner pressure.
The minimum and maximum burner pressures must be set after
a new gas control has been fitted.
Follow the procedure described in Section 13.4 - Appliance
Operation.
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 13.4. - Appliance Operation.
Turn the gas valve mode switch on the rear of the facia to
maximum.
Adjust the maximum pressure adjustment screw on the gas
valve to give a burner pressure of 13.2 mbar for natural gas.
Turn the gas valve mode switch on the rear of the facia to
minimum. Adjust the start pressure adjustment screw on the gas
valve to give a pressure of 2mbar for natural gas. Turn the gas
valve mode switch on the rear of the facia back to normal.
After completing the adjustments, check the minimum and
maximum pressures and re-adjust as necessary.
It should not be necessary to alter the central heating
potentiometer setting when the gas control is replaced and the
minimum and maximum burner pressures are set.
10. Central Heating Sensor.
Refer to Fig 28.
Remove the inner casing cover as described in Section 15.3, b.
Check that the electricity supply to the appliance is turned off.
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.
11. Domestic Hot Water Sensor.
Refer to Fig. 30,33.
Check that the electricity supply to the appliance is turned off.
Hinge the facia panel into the servicing position as described in
Section 15.3, c.
Carefully pull off the two leads from the sensor.
Undo and remove the screw, pull off the sensor and spring
retaining clip from the pipe.
Fit the replacement sensor in the reverse order ensuring a layer
of heat sink compound is between the faces. Refit the leads.
12. Circulating Pump.
Refer to Figs. 30,31.
Check that the electricity supply to the appliance is turned off.
Drain the central heating circuit as described in Section 16.3, a.
Hinge the facia panel into the servicing position as described in
Section 15.3, c.
Undo the two union nuts and the pipe to the expansion vessel,
remove the pump from the pipe-work. Support the pump and
remove the electrical cover.
Disconnect the electrical wires taking note of their positions.
Fit the replacement pump in the reverse order using new sealing
washers.
Alternatively
replace the pump head only by removing the four
Allen screws on the pump, remove the head and support whilst
removing the electrical connections. Refit the new head.
Open the valves and fill and re-pressurise the system as
described in Section 13.2.
NOTE:
The direction of flow should be downwards. The speed
should always be set to maximum.
Fig. 29. Combustion Chamber Insulation
Combustion chamber front and
side assembly
Side insula-
tion
pad
Side insula-
tion
pad
Front insulation pad
When reassembling ensure these
locations are correctly fitted in the
slots at the rear of the inner casing
View from inside the combustion chamber
20
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