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13 Fault Finding
7402
Check appliance installation and
that it is mechanically correct.
YES
Check filters are clean and allow
adequate water flow.
YES
NO
Check fuses and power supply.
Is mains L.E.D. illuminated.
YES
Open a tap to create demand.
YES
NO
If lockout L.E.D. is illuminated, press reset.
YES
A
NO
Demand L.E.D. illuminated.
Check flow switch operation.
YES
B
NO
Pump starts.
Check the pump is not mechanically stuck.
Check 230V supply to pump.
YES
C
NO
Fan starts.
Check air pressure
switch operation.
Check 230V
supply to fan.
Check thermistor.
Unplug fan and check
coil resistance.
YES
D
NO
Start spark.
Check spark electrodes
and cables.
Check primary circuit
overheat continuity.
Check air pressure switch status
and operation.
YES
E
Gas control valve opens at
ignition rate (5-6 mbar).
NO
Check gas control
valve cables.
Check gas control
valve voltage.
Check venturi and
connecting tubes.
YES
F
Burner pressure increases
to full rate.
NO
Goes to lockout.
Check sensing electrode
and cables.
Check burner for
cross lighting.
YES
G
Turn control thermostat or flow
rate down to induce modulation.
NO
Is heating circuit
getting hot.
Check 3 way
valve operation.
YES
Manually push brass splindle in diverter
valve. Does domestic hot water get hot
when pushed in and central heating
water get hot when released.
Domestic hot water operates.
YES
Unclip motor. Turn domestic hot water
Off and On. Does pin move in and out.
Switch to central heating demand.
YES
NO
Demand L.E.D. illuminates.
Replace motor.
If domestic hot water demand is still illuminated.
Faulty domestic hot water switch.
YES
Follow B-G.
YES
Correct operation.
Diagram 13.3
221895A
30