Boiler Problems

[slid_away]

Hi All
We have a Glo-worm condenser boiler. We tend to leave this on 18 degrees on the thermostat and let it come on when the temp drops below that.
Just lately I have noticed that the house is cold even though the the bolier appears to be on.
On closer inspection, I listen to the boiler come on, the fan kicks in and it ignites, no problem. After about a minute, I hear a clicking sound and the boiler seems to ignite again. This happens for as long as I am listening for it. It seems to be struggling to stay ignited.
The only thing that helps is, if I turn the boiler off for 20 - 30 minutes and then put it back on, the rads will get hot but as soon as the thermostat cuts in to switch it off, when it tries to come back on again once it has gone below 18 degrees, this is when the problem starts.
An engineer is coming out sometime this week but if anyone knows what this is and if they have had the same problems as me I'd be grateful to know what the problem is.
Many thanks in advance

[The Builder]

Do you mean you have the roomstat on the wall set at 18, or the boiler temp?

[slid_away]

Its a wall set thermostat that we keep at 18 degrees. The boiler it's self only have a dial with low or high flame.
Cheers

[The Builder]

AlBags knows more about these than I do. He may be along later.

So many possibilities. Gas supply possibly being cut off by a faulty sensor; boiler thermostat maybe.
I wouldn't have thought there is anything you can do until its checked out though :o(

[slid_away]

Thank you mate, appreciate your answer

[slid_away]

Anyone have any ideas please?

[AlBags]

I'm here .. and thinking about it.
This is called cycling .. Due usually to no water movement through boiler (or insufficient) OR a boiler component fault .. like thermostat as TB said, or even the circulation pump not starting/sticking when hot.

When it is hot (rads warmed) exercise the room stat to 'call for heat' (turn up) and check the pump runs .. feel or listen to it.
Make sure any water temp setting in boiler panel is set well up.
Report back!

[slid_away]

Sorry Albags, I've been offline for a week and only just seen your post.
Well I tried what you said and the pump seems to be working fine.
I did have an engineer come out during the week and would you believe, it didn't do it the whole time he was here!! He was at my home for an hour and a half and we tried the firing up the boiler numerous times to no avail. I did manage to record it on my Iphone and he said it could be a gas valve sticking and the noise does certainly seem to come from there (where the gas valve is)
Thank you for taking the time to give me a answer, your expertise is very much appreciated.
Many thanks The Builder and Albags