my worcester 350 is going over pressure to nearly 4 bar. There is water coming from the pipe outside. I have turned the radiator temperature down to min but its still the same.

Nob, November 2008

it was the expansion tank, the engineer said about 5 to 6 years out of one. Mines laster 17 so its done good, thanks for the answers and the diagnosis.

Nob, November 2008

the filling loop is still conected,and still fills the system which is stable untill the heating is used. I have a worcester engineer coming thursday so will add the result. I'm guessing at the expansion tank..

Nob, November 2008

has it got a filling loop still connected? when it fails you get the symptoms you describe. if so need not cost the earth to fix.

plumbersw15@talktalk.net, November 2008

Your secondary heat exchanger is the most likely cause (if pressure builds up when system is cold..not in use) if not it will be the expansion vessel.Best to also change the safety valve at the time of repair.Do Not use anyone who is not competent with these boilers...Not a cheap fix but a poor engineer will cost you a lot more money

chris(ex gas engineer 30 years), November 2008