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12 Fault Finding
Fault Finding
12.1 Boiler Fault Finding
Always isolate the electricity supply to the boiler before working on the boiler.
Fault
Boiler will not start: Remedies
1 No fuel supply.
2 No electricity supply.
3 Burner not starting - fuel and
electricity supplies present.
4 Burner lights but goes to lock-out.
Ensure that an adequate supply of fuel is available and that the fuel supply valve is open.
Check the condition of the fuel filter, clean if necessary.
Ensure fuel supply is reaching burner and vent pump.
Ensure electricity supply to the boiler is switched on and that all controls are calling for heat.
Ensure that the overheat thermostat has not tripped, reset if necessary.
Check that a mains supply is present at the burner terminal block.
If not, check the boiler and overheat thermostat.
Press the reset button on the burner control box if it is lit.
Refer to burner fault finding charts.
If the flame is unstable, check the combustion settings.
Refer to burner fault finding charts.
Boiler works but:
Insufficient air supply - check the air damper setting and the condition of the fan.
Check room ventilation is adequate, see Section 9.1.
Check the nozzle size and type.
Fuel pressure may be too high - check and adjust.
Insufficient air supply - check the air damper setting and the condition of the fan.
Check room ventilation is adequate, see Section 9.1.
Check the nozzle size and type.
Insufficient air supply - check the air damper setting and the condition of the fan.
Check room ventilation is adequate, see Section 9.1.
Check the nozzle size and type.
Fuel pressure may be too low - check and adjust.
Insufficient draught - clean boiler heat exchanger and check condition of flue.
Undersize nozzle and/or low fuel pressure.
Check condition of boiler heat exchanger and clean if necessary.
Check the boiler thermostat.
Check the combustion settings.
Check the condition of the fuel filter.
Faulty boiler thermostat. No circulation, check circulating pump. Check for air lock.
Check the condition of the chimney, ensure it is not blocked and is high enough to produce the
required draught. Check that there is an adequate air supply near the burner and that a kitchen
fan is not drawing products out of the burner.
Check all fuel line connections, remake as necessary.
Check boiler cleaning cover and seal are correctly fitted.
Check burner is correctly fitted onto flange.
Check flue is correctly sealed into flue outlet of boiler.
Check the condensate pipe and trap are operating correctly.
5 Visible smoke from flue or high
smoke number.
6 Burner pulses.
7 Flame slow to stabilise
during start up.
8 Water temperature low.
9 Boiler operating on overheat
thermostat.
10 Fumes and puffing during starting
(conventional flue)
11 Oil odours.
12 Combustion fumes smell.
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