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© Baxi Heating UK Ltd 2012
18.0 Fault Finding
Check and correct if necessary
1. The mechanical set of the gas valve
(CO2 values - see instruction)
2. Flame sensing electrode and lead connections
3. Flame sensing electrode position
Flame current should be more than 0.5 A
Replace PCB
Replace PCB
YES
YES
Replace flame sensing electrode
NO
Check supply pressure at the
gas valve:-
Minimum 17mbar
I
K
Replace safety thermostat
YES
NO
Overheat thermostat operated or
faulty, i.e. continuity across
thermostat terminals
Allow to cool. Continuity
across thermostat terminals
more than 1.5 ohm
J
L
M
Is there 230V at:
Motor 3-way valve Replace motor 3-way valve
1.
YES
PCB - X3 connector terminals
5 & 6 central heating mode
5 & 7 domestic hot water mode
Replace PCB
2.
NO
Change pump supply cable
YES
Fan connections correct at fan.
PCB - X401 connector terminals 5,6,7 & 8
1.
YES
Replace fan
Temperature sensors faulty.
Cold resistance approximately
10kí @ 25° C (CH sensor)
20kí @ 25° C (Flue sensor)
(resistance reduces with increase in temp.)
NO
Replace sensor
YES
If pump is running the heat exchanger could be
obstructed
Replace heat exchanger
1.
2.
1.
2.
1.