Very useful to have these forums, so can anyone please help, or is it the changeover valve, as someone else's problem was..?
The heating works fine, but when hot water is demanded the boiler fires as normal yet doesn't produce any!
It's in a rental property and although the tenants are very patient and understanding, I want to get it fixed ASAP.
Could it ONLY be that valve, or something else? Is it easy? Expensive? Can I do it? Where would I get the required part?
Many thanks for any help...
Cheers,
Nick

Nick, October 2008

Thanks Brendan. Changed the whole valve, which, amongst lots of other tweaking - including changing the hot water potentiometer, hot water thermistor and reducing the flow of cold water to the boiler - sorted it all out. I'm now a fully-qualified Saunier Duval engineer...!

Nick, December 2008

Diaphragm. Hot water not turning on. To prove this turn off the heating, turn on the tap and nothing should work.

Bendan, November 2008