Is it the thermocouple ?

[Kevin]

I have been having problems over the last couple of months with the pilot light going out on my Glowworm SpaceSaver 50 Mk II boiler. It started out happening every now and again and has got gradually worse. What's happening now is that I can light the pilot light, and the main burner fires up ok, but when the main burner switches off again after a few minutes, the pilot light is also extinguished at the same time. I am probably going to replace the thermocouple but is there likely to be anything else I should be looking at ?

Thanks.

[Christian McArdle]

Personally, in that situation I'd change the thermocouple first and ask questions later, if that doesn't fix it.

Christian.

[Bob Mannix]

It's nearly always the thermocouple. The universal ones you can get in B&Q will usually fit (they fit my Glowworm anyway). I have replaced about 2-3 in

8 years

[Dave Plowman (News)]

If you can remember, is the pilot light rather weedy compared to before? If the boiler is lighting, it means the thermocouple is working. Could be the slight pressure change as it lights blows the pilot light out. Cleaning the pilot light jet would be my first try.

[Set Square]

Can you please clarify what the "after a few minutes" refers to.

Do you mean that the main burner runs for a few minutes and then stops, and that the pilot goes out at the same time? [I think this is the one you mean]

Or do you mean that the pilot remains lit for a few minutes after the main burner stops, and *then* goes out? [I wonder whether others have thought you mean this]

If the pilot is going out with the main burner, it suggests that it's being blown out by the draft caused by the main burner shutting down. This could be because it is not very strong - possibly because its jet is partly blocked by crud, or because it needs to be adjusted up a bit. [Does it have its own regulator, to adjust the height of the flame?]

Does the pilot remain lit indefinitely if the main burner isn't running? If so, it's unlikely to be the thermocouple at fault.

[kdband]

Yes.

I could certainly believe this as I've been doing a lot of work creating a lot of brick dust etc., but I did attempt to clean it last night and it still didn't work.

I don't think so, but I will check again.

Not sure I gave it long enough to be certain but this was certainly my impression.

I bought a new thermocouple at lunchtime which I will be fitting tonight (at =A32.50 plus VAT for a universal one it was silly not to). I'll let you know if I still have problems after fitting it. Thanks for all the responses.

[Dave Plowman (News)]

If the thermocouple was faulty, surely the main gas valve wouldn't open at all?

I'm only on my second. In about 25 years.

[kdband]

Well I replaced the thermocouple last night and cleaned the jet on the pilot light again. It took quite a while to get the pilot to stay lit but the flame was much stronger than it had been previously. It did work well for quite a while last night and did stay lit even after the main burner had shut down again, but there was one occurance of the pilot being extinguished again. Not sure when it happened as I wasn't watching it constantly. I relit it again and it seemed to work after that and was still working this morning even though the timer had switched the heating off and then back on again overnight. I'm keeping my fingers crossed but I'm not yet convinced I've got to the bottom of the problem.

[Set Square]

Well, the flame being stronger *has* to be the result of cleaning the jet - the thermocouple wouldn't affect this.

I suspect that the root cause of your problem was a weak jet - so let's hope it will now work reliably.

[nick smith]

I had exactly this problem on a Glow worm 50,000 BTU 4 days ago - the Band Q universal thermocouple did the trick (original part was £15 locally !!) but I also noticed that the pilot flame was unstable and found a load of corrosion had broken away from the burner frame and fallen down the burner tube, partially blocking the pilot jet - cleaning this out also made the flame fairly stable and adjusting the flame splitter so it engulfed the thermocouple tip must have helped too.

Nick

[Set Square]

Geting rid of the crud would probably have worked without changing the thermocouple.

[nick smith]

You may well have been right, but as I had it all apart an extra three quid was minimal to save having to think about changing that.....

Nick

[Kevin]

Well mine has been working fine now for nearly a week. I agree with Nick, given the cost of a new thermacouple it isn't worth not replacing it even if it may not have been strictly necessary.

[Dave Plowman (News)]

But you'd have to go and get one.

If the pilot light is reduced in size for whatever reason, sort that first.

[Set Square]

Absolutely! And if you replace the thermocouple when there's nothing wrong with it, but fail to address the *real* problem, you won't be any further forward.

[bob]

Hi The thermocouple range is usually 8 to 15 mv and can be measured using a candle for the heat, But changing a thermocouple has to be done properly and what 99.9% of installers fail to do is to clean out the gas block connection with a brass brush, The thermocouple tube has a alloy outer olive (the neg?) this leaves oxide in the gas block reducing the quality of the contact. Maplin have a PCB cleaning brush which is ideal Regards Bob