My Worcester bosh boiler for some time now has been losing pressure and letting out water from the release valve (the pipe outisde the house. Have had a heating engineer out and and they have changed the expansion vessel, whilst this has solved the problem of pressure I now have a new problem.........When I fire up the heating and it has run for half an hour or so I am now getting the fault indicator light flash at me, whilst this is flashing I am not able to get any hot water as the boiler will not ignite. Once I have reset the boiler and it cools off I am then able to switch heating on and have hot water on demand. Any one have any idea's as my enginner seems to think I need a new heat exchanger and this is very costly to fix and I would be wiser putting in a new boiler, but my boiler is only 5 years old. SOMEBODY PLEASE HELP!!!

Rachel, November 2010

Bit late now, but bosch have crap air pressure switches, these cause tricks like this, tell tail click can be noticed about a second or two before burnner shuts off. 25 quid bit anyways, worth trying first.
Crack in plastic pipes from fan can do same as the pressure switch looses pull as they warm up, had that to.

w wils, January 2011

Numerous possiblities I'm afraid, they do include the heat exchanger, it sounds like an overheating fault if you get heating for 30 minutes before shutdown:
Pump running slowly/sticking
Flue obstructed (causing fps to shut down)
Condense obstructed
Flue overheat stat problematic (most likely caused by the above two)
Main heat exchanger collapsed (if the heat exchanger is ribbed and not smooth)

Carefree, November 2010