Technical information

49
Combi 70 & Combi 90 Oil Boilers
11 - FAULT FINDING
No water flowing from hot tap
Mains water supply is not connected to cold water inlet of boiler.
One or more isolating valves, stop cocks, etc. in the pipework are closed.
The cold water isolating valve in the boiler is closed.
There is a blockage (or blockages) in the pipework.
Hot tap is not connected to hot water outlet of boiler.
Insufficient flow of water through boiler.
Boiler cold water and hot water connections reversed.
Thermostatic mixing valve incorrectly fitted.
Pump is not operating in hot water mode.
Diverter valve microswitch(es) faulty.
Diverter valve microswitches not operated.
Diverter valve seized.
Diverter valve diaphragm failed.
Boiler thermostat incorrectly set
Thermostatic mixing valve incorrectly set.
Faulty store thermostat.
Pump speed setting too low.
Pump is incorrectly fitted.
Burner not firing for hot water.
Burner fires, but not within 90 seconds of hot tap being opened.
Burner oil pressure set too low at oil pump.
Incorrect oil nozzle fitted to burner.
Check and rectify as necessary.
Open all valves in pipework to and from boiler.
Open valve (situated below plate heat exchanger).
Check and rectify as necessary.
Check and rectify as necessary.
Open tap to increase flow.
Check and rectify as necessary.
Check hot and cold inlets are connected correctly.
Check operation of diverter valve.
Check pump is free to rotate and is vented.
Check power is present at pump terminals.
Check electrical continuity of pump microswitch.
Check wiring continuity from pump to microswitch.
Check switch continuity, replace if faulty.
Check diverter valve diaphragm.
Remove, dismantle and clean.
Replace diaphragm or complete diverter valve.
Set boiler thermostat to maximum.
Set mixing valve to setting '4'.
Check continuity and replace if necessary.
Set pump speed switch to maximum (top position).
Check and rectify as necessary.
Check operation of burner on central heating.
If burner faulty, refer to burner fault finding chart.
Check store thermostat is set to 75 to 80°C.
Check electrical continuity of burner microswitch.
Check electrical continuity of store thermostat.
Check operation of diverter valve.
Check wiring continuity from burner to microswitch.
Set oil pressure to correct value (see section 2.2, 2.3).
Fit correct nozzle (see section 2.2, 2.3)
No hot water operation
(no response when 3 litres/min or more
is drawn off at hot tap).
FAULT
POSSIBLE CAUSE
ACTION
Hot water for short period only
Low water temperature at tap
Central heating OK - poor or no domestic hot water
11.1