i have a potterton kingfisher 2 floor standing boiler when it is on number 6 or on number 1 the heating and hot water are boiling. hot rads to hot to touch that the paint is cracking it will not turn up or down the tank in the loft is constantly bubbleing and its only on 2 hours if that can any one give me a clue what is wrong. my boiler is serviced every 2 or 3 years i did mention it to him but he did not seem to know what was wrong i will thank you now for your help and advice