Boiler noise on glowworm

Hi,
I don't know if anyone can help me.
I have a glow worm combi boiler and it is making a noise.
When the central heating comes on, it is ok for about the first 10-20mins then it starts making a noise and the gas goes out then the noise stops and the gas comes back on. it does this for about 10mins intermittently then after that it runs fine.
It does it every time the heating comes on.
I can't really describe what the noise is, it sounds like something is getting stuck the frees up. I thought It was the timer but this has been replaced.
Can anyone shed some light on what it might be?
Thanks.

I have a glow worm combi boiler and it is making a noise.

Click to expand...

well that narrows it down to 20 or so

bit more info

Hi,
Sorry, had to dig out the instruction manual.

It is a glow worm compact 75e combi boiler.

Update on the noise, it sounds like a chattering/clicking noise.
It sounds like it is coming from around the section that you flip down to get to the controls/timer etc.