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10
Maintenance
Combustion
Control Unit
Fig. 54
Fan Protective
Cover
Electrical
Plug
54
600 Heat
Press the tab to
hinge down the
Fan Protective
Cover
Fig. 53
PCB
Fig. 55
Gas Inlet
Pipe
Fig. 56
Fig. 57
10.3.10 Combustion Control Unit (Figs. 53 to 57)
After replacing the Combustion Control Unit the CO 2
must be checked and adjusted as detailed in Section
10.3.11 Setting the Gas Valve. Only change the
Combustion Control Unit if a suitable calibrated
combustion analyser is available, operated by a
competent person - see section 10.1.3.
An ESD wrist strap should be used when replacing
these components.
1. Ensure that the gas supply to the boiler is isolated.
Remove the ducts as described in Section 10.3.4
2. Disconnect the cable from the bottom of the PCB, disengage
the fan protective cover securing tab and lower the cover after
disconnecting the electrical test point (Figs. 53 & 54)
3. Taking care not to touch the PCB components, disconnect
the electrode lead, earth lead, mains power cable and the main
sensor harness from the board. Re-engage the fan protective
cover (Fig. 55).
4. Disconnect the plug from the gas valve and undo the nut on
the gas inlet pipe at the base of the valve (Fig. 56).
5. Remove the combustion control unit from the boiler by
releasing the over-centre catches that secure it to the heat
exchanger (Fig. 57).
6. Reassemble all components in reverse order. When a seal
kit is provided replace the existing seals with the new ones.
Inspect all other seals before reassembly and replace if
necessary. Check all the joints are tight and wires are securely
connected.
Check gas tightness & CO 2 !
If the boiler will not light, prior to final setting, use a
suitable hexagon key to wind out the Throttle
Adjustment Screw until it is flush with the valve body,
then turn the screw 4 full turns clockwise. If the boiler
will not light, or the correct CO 2 cannot be achieved
contact the 'Baxi Customer Support' technical helpline.
See Section 10.3.11 for CO 2 check.
7726858-01 (1/19)
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