Can you help with an indicator lamp on a Worcester R 29 / R 40 HE?

Question from Dulcie Brookfield,via email:
The indicator lamp for the burner on my Worcester R 29 / R 40 HE conventional condensing boiler has gone off and I can’t get any central heating.

Can you give me some advice on how to get it working?

Answer from Martyn Bridges, director of marketing and technical support at Worcester, Bosch Group:
Has the work being undertaken involved the replacement or repositioning of any of the heating and hot water system pipework or is it confined to the ?

My reasoning behind the question being that if a noise occurs after several hours of boiler use, i.e. the boiler is up to temperature I wonder whether any of the system pipework perhaps containing any system bypass has been altered preventing any pump over-run or circulation?