Fault Finding
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2.2 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. 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.
2 No electricity supply. 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.
3 Burner not starting - fuel and Press the reset button on the burner if lit on the control box.
electricity supplies present. Refer to burner fault finding flow diagram.
4 Burner lights but goes to ‘lock-out’. If the flame is unstable, check the combustion settings.
Refer to burner fault finding flow diagram.
Boiler works but:
5 Visible smoke from flue or high Insufficient air supply – check the air damper setting and the condition of the fan.
smoke number. Check room ventilation is adequate. See Section 9.1.
Check the nozzle size and type.
Fuel pressure may be too high – check and adjust.
6 Burner pulsates. 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.
7 Flame slow to stabilise Insufficient air supply – check the air damper setting and the condition of the fan.
during start up. 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.
8 Water temperature low. 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.
9 Boiler operating on overheat Faulty boiler thermostat. No circulation, check circulating pump. Check for air lock.
thermostat.
10 Fumes and puffing during starting Check the condition of the chimney, ensure it is not blocked and is high enough to produce
(conventional flue). 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.
11 Oil odours. Check all fuel line connections, remake as necessary.
12 Combustion fumes smell. 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.
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