Hi. I'm repairing my boiler after it froze. I have the central heating working now (pump and flow sensor damaged), but when I turn on the mains water to the boiler it pressurises the system until it reaches over 3 bar then fires the blow-off valve. The loop pressuriser works normally.
If the water isn't switched on the hot water taps work (!) but uses up the heating pressure. This boiler is the one without the diverter valve, so I suspect there is a breakdown within the heat exchanger though there is no leak. Is this likely or have I missed something?
Thanks!

Glyn, December 2010

You've crossed a pipe somewhere.

Carefree, December 2010

Which is why you shud never b allowed to work on things u don't understand and r not qualified to work on!

PP, December 2010