Worcester Greenstar R25 HE Combi burner problem?

Hi there,

I have just bought a new house and have a problem with my boiler and thought I may be able to get some advice on here rather than calling someone out if the problem is simple. I apologise in advance if I sound clueless...I am!!

It's a Worcester Greenstar R25 HE Combi. The hot water runs fine but when we put the heating on, the burner light doesn't stay on and the heating just clicks on and off so the house never seems to get warm.

Can anyone help me with what the problem might be?

Thanks in advance,

Jennie