We have a worcester 28 CDI boiler and have had an ongoing problem. If we turn up the thermostat or demanding hotwater, the boiler fires, then after 5 seconds theres a ticking noise and a clunk.

Removal of the cover shows that the boiler fires and the rad or water light comes on but the flame light does not. It ignites and all is well, then 5 seconds later the ticking noise is the boiler sparking again (even though it is already lit) and then the whole thing stops. and the red radiator light flashes. To start the boiler we press the reset button and then it fires up as it should but this time the flame light is on and then it works fine.

Ive had a local heating engineer out who replaced 2 components that were leaking and the PCB which showed a burn mark on a capacitor - testing this component on the PCB with a multimeter showed it wasnt a complete circuit however it had been working (somehow) when previously installed.

Co currently Im facing a £600 ish bill and its still got the same fault.

Has anybody got any ideas?

Colin, February 2009

get corgi guy to clean the flame electrode

stedo, February 2009

If we'd got Worcester out it was goint to cost £210 for something that I believed to probably be a cheap part.

As it turns out they arent cheap parts - on the other hand Worcester only repair/replace (I believe) a maximum of 3 parts and when I spoke to them they said that an engineer could say it was beyond economical repair. So I could have paid that and have them say it was beyond repair and faced with fitting a new one at around (i'm guessing the £2k mark) I dont think (so far) I've made a bad judgement on this - £600 I cant afford, £2k I really cant afford ;)

So far we have had 3 componenets replaced. 2 components were leaking and the board had a burn / partial dead circuit on 1 cap or it may have been a resistor. A multimeter test proved this It appears it was somehow still working with this dead circuit when it was originally in though - Im unsure as to how but hey ho.

Anyway so far, it now appears to work (apart form the initial glitch after the parts had been replaced and the boiler refilled) and im told it may have been an airlock in the system that was causing the problem.

Could that be right then, that an airlock would cause the boiler to try an re ignite after it was already lit, fail and shut down or go into a mode where it needed to be reset. It's happened twice in a row after fitting and been fine since!

All I can say is the proof is in the pudding and so far its fired up correctly by itself 7 or so times whereas before it would have always required a reset before working as it would ignite, fire then reignite then shut down and have to be reset. EAch time it was going to fail the flamelight didnt come on. Then a reset and it would work.

I appreciate and helpful comments

Colin, February 2009

£600?! Could have got Worcester out to it for half that, parts included.

Bunslinger, February 2009

sounds like the flame detect lead / electrode are faulty

Paul the gasman, February 2009