Hi, can any one help me? When I switch the boiler on it will initially light and after a few minutes the main burner goes out. The pilot light is staying on and is not sparking. It did light and run today for an hour and then went out and would not relight. I have a grundfoss circulating pump which is running and have individual thermostats on the radiators. The motorised valve was set on heating and hot water but has now turned round to CH only. Is this because I have put the immersion on for hot water? The control box is a Potterton EP2001 and the switchable valve is a switchmaster. It was working OK one day then nothing the next. When it tries to fire up there is sometimes a clicking noise from under the boiler. Have checked the reset button and it is not that. Any help greatly appreciated. Its freezing!