Boiler not firing up - intermittent problem

[Battenburg]

Hi,
Thanks for reading this.
I am looking for some advice, as a boiler engineer has had an initial look at our system and is not sure of a solution. We have an Icon 24t combi-boiler that is at least 10 years old and frequently will not fire-up properly (for both hot water and heating). The problem is getting slightly worse each day, and seems much more likely to occur when trying to use the boiler within about 30 minutes of a previous use. When it occurs, the boiler is clearly "trying" to light - it clicks, tries to fire, but fails - it then continues doing this indefinitely until it is turned off. After keeping it turned off for 30-60 minutes or so it will then usually (but not always) fire-up without a problem.
Any thoughts would be appreciated, as the only idea so far is to try and replace the PCB (although he admitted that this may not solve it).
Thanks!

 

[anz]

From what you say, to me it sounds like the gas valve, (solenoid).

 

[Battenburg]

Thanks anz - I am assuming that the gas valve controls the flow of gas and electrically opens when the boiler needs to fire. Do they fail instantly, or could they be intermittent (and possibly more likely to stick when hot/warm?).

 

[anz]

Yes you are right. Its very common for the solenoid to fail for a short period of time before starting to work again. It will eventually fail if this is the case.

Your Gas Engineer should confirm that this is the fault by testing it when it is in the failed state.

Intermittent faults like these can also be caused by the PCB, like your engineer says.

 

[Battenburg]

Cheers anz - if he comes out again I will ask him specifically if he has tested the gas valve. I think that I had assumed that it could not be the PCB if it was intermittent (i.e. they would just break or not) - I think he quoted £200+ for the PCB, I am guessing a gas valve would be slightly cheaper. I also assume neither is a DIY job.

 

[anz]

I would definitely not recommend you to DIY.

I don't have a clue how much a gas valve is for these boilers, but generally speaking I think your looking at a similar sort of price, slightly less, maybe.

 

[Battenburg]

Thanks for your help - either PCB or gas valve - fingers crossed that he can get the right one first time!

 

[pmac10]

i only work on industrial gas burners on the maintenance side of things, but from what you describe, the click you hear is probably the gas valve opening. once this happens a flame must be detected within a set time otherwise it will lockout or attempt a restart, i would start with your flame detection, probably a UV cell or IR detector and establish if this is working correctly before replacing a PCB on a whim.
this is how our various types of burner all operate and i assume domestic ones would be the same.

 

[Battenburg]

Very useful reply pmac10 - it makes sense that there must be some kind of sensor (or safety cut-off) that would keep the valve open (I had thought this would be heat based, but thinking about it that would not be quick enough to repsond). I will have a look at the manual again later, and see if I can identify a possible culprit. I do have reservations about allowing the replacement of £200 components on a trial and error basis!

 

[gasmarc]

i would defo not replace anything until I found the fault ,the first thing i would do is check the spark electrode is clean and is has the correct gap as this will cause all types of faults

 

[Battenburg]

I agree I would rather not pay out for a replacement before diagnosing - but then I would also rather not pay a fortune for an engineer to spend hours trying to diagnose (that is why this kind of forum is so uesful to me/customers to provide some short cuts, offer ideas and give you a chance to know roughly what the experts are talking about!). Thanks for the help.

 

[Battenburg]

Thinking about it, I am not sure that the the spark electrode would be the problem - it seems to "fire" briefly (ie less than a second), but then stop (as though the flame is not being detected as suggested by pmac10). I am guessing that if this was faulty then it would not fire at all? (my original description of the problem may not have been detailed enough).

 

[Battenburg]

Final update. An engineer came out again - apparently, and as far as I can confirm second hand, it was the smaller PCB (that is just before the spark electrodes I think). He has replaced it with one that he had in the van, and now everything is working fine!

NB: BTW - it was actually an Icon 23t (not 24t as I said).

Thanks to everybody who took the time to reply - much appreciated.

 

[diesel_ltd]

good to get a final update on boiler faults, good luck with your boiler in the future

Final update. An engineer came out again - apparently, and as far as I can confirm second hand, it was the smaller PCB (that is just before the spark electrodes I think). He has replaced it with one that he had in the van, and now everything is working fine!

NB: BTW - it was actually an Icon 23t (not 24t as I said).

Thanks to everybody who took the time to reply - much appreciated.