Doc No. 700070 Page 50 of 56
6. Fault Finding Guide.
Symptoms
Possible causes
Remedy
Vacuum fan is running
but there is no power at
burner. Neon lights are
off.
Thermostat is satisfied.
Check to see that thermostat is calling for heat.
No power at burner.
Check for 240V supply.
Blown fuse in supply to heater.
Check and replace if necessary.
End vent vacuum too low.
Vacuum at end vent should be 6.25 mbar (2.5in
wg). Check for air leaks on burner.
Air pressure switch on end vent burner not opening. Check and replace if necessary.
3 way air valve (if fitted) in end vent burner not
opening.
Check and replace if necessary.
No power out from end vent burner.
Check for loose or broken wire or faulty relay.
Red neon comes on but
ignition sequence does
not start and amber neon
remains off.
Loose or broken leads to sequence gas controller.
Check and repair.
Fault in full sequence gas controller.
Replace.
Red neon comes on.
Amber neon comes on
for ignition period; then
amber neon goes off.
No ignition spark.
Check for loose or broken high tension lead to
spark electrode.
Check spark gap and position for spark
electrode.
Check ceramic is not cracked.
Check for loose earth wire connection on
sequence gas controller.
Fault in full sequence gas controller.
Replace.
Insufficient gas supply to burner.
Check service cock is open and gas pressure is
available at inlet to gas valve.
Gas solenoid valve not opening.
Check for loose or broken wires to the gas
valve. Check for adequate end vent vacuum.
Replace valve if necessary.
Injector pressure not set at zero.
Check and adjust.
Incorrect aeration.
Check that air shutter plate on mixing chamber
is correctly positioned.
Red neon comes on.
Amber neon comes
on for ignition period,
burner lights for a short
time and then goes out.
Amber neon off.
Flame probe faulty or lead detached.
Check for broken ceramic. Check for correct
position of flame probe.
Fault in sequence gas controller.
Measure flame current.
The minimum signal is 3μA (DC).
Polarity of line and neutral incorrect.
Check for correct polarity of the electrical
supply.
Burner earth is poor.
Check and ensure burner is correctly earthed.
Full sequence gas controller faulty.
Replace.
Incorrect aeration.
Check that air shutter plate on mixing chamber
is correctly positioned.
End vent vacuum too low
(ie below 6.25 mbar (2.5in
wg). Check section 3,
commissioning for exact
vacuum details.
Branch damper closed or broken.
Open branch damper until the correct end vent
vacuum is achieved .
Replace damper if necessary.
Fan rotation incorrect.
Reverse two phase wires on 3 phase motors.
Fan speed wrong.
Check voltage at motor. Replace if necessary.
Fan impeller loose or defective.
Tighten or replace if necessary.
Restriction to fan inlet.
Clear restriction, repair flue duct.
Air leaks into system via poor joints.
Replace defective tube couplers, gaskets or
acoustic joints.
Insufficient fall of system towards fan
allowing condensate blockage.
Reinstate system fall.
Non return valve sticking open on
condensate trap assembly.
Clean valve or replace if damaged.
