When running a bath the boiler runs fine to start with then suddenly the pressure shoots upto to about 3 bar, lots of clanking a banging from the boiler and the pressure valve blows on the top of the boiler. After about 10 mins all is fine again.
What would cause this?

Adam, October 2008

Have now been told that this is the diverter valve and a common problem on this boiler. Just need to find a plumber that does turn up when he says he will!

Adam, November 2008