Pilot light keeps going out but only when boiler is warm

8 Oct 2019
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United Kingdom
Please note that I'm posting this question just to get a better idea of what the problem could be and how much I should expect to pay a professional to fix this issue for me, I do not intend to try and fix this problem myself...

I have a very strange problem with my Glowworm Ultimate boiler, in that if the boiler is cold and I switch it on, the pilot light comes on, stays on and the boiler kicks in fine. However, after around 20 minutes, the pilot light starts going out every few seconds and the boiler sparks to re-ignite the flame. It's a blue flame, I can't see any orange.

If the boiler has already been on for a while and I then turn it off for 15 minutes or so, then turn it on again, it ignites the pilot light fine and it doesn't go out, however after around 5 minutes or so, I then have the same issue with the pilot light going out every few seconds again.

It's as if the issue with the pilot light is dependant on how warm the boiler is.
Could this indicate that the thermocouple needs replacing?

Thanks for any assistance!
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Which model of Ultimate is it? There have been several! Is it the one with the grey controls cover at the bottom? If it is, there's a data plate on the inside of the right hand casing panel....

I did have this with such a boiler a couple of weeks ago and it was a partially blocked pilot. A good service cured it. Might not be the issue you have though!
Hi Andrew, thanks for your reply.
My boiler looks to be the same model as this one:

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