Combi boiler ignites, but won't stay lit, flame detection?

shinjukumaster

Its an old ICI Caldaie 120SE, serviced last year, PCB & air switch replaced. CH is on a timer, didn't come on this morning. For CH or HW the boiler will fire up OK, but only runs for 10-20 seconds, the igniter fires again, as if its not seen the flame detect, flame is extinguished, then it goes into lockout (red lamp on). After reset it will start again, but repeats the same cycle. I can see the flame through the spyhole for the duration it is lit.

It uses two igniter electrodes, and one flame detect sensor. Is it likely that the sensor is faulty? Or PCB trouble? Is there any way I can check that out with a meter?

[Deleted User]

Have you been bleeding your radiators? You cold have low water pressure. Is your pressure needle below '1'?

http://www.ultimatehandyman.co.uk/TOPPING_UP_A_COMBI_BOILER.htm

shinjukumaster

Radiators have been bled. Pressure OK.

I forgot to add that what I'm seeing is the ignition sparking again, after the burner is already lit. Burner runs for approx. 15 seconds, then the ignitor sparks again. It retries and goes into lockout.

shinjukumaster

OK, I found the problem. The end of the inner tube on the flue had dislodged very slightly at the outside wall. Possibly a combination of freezing temps, and vibration. Its now secure and the boiler is running fine again.