"Frank Erskine" wrote in message
...
I'm having a spot of bother with the above.

When the heating is running, the only DHW that I can get is a few
seconds of warm water then cold (clearly the hot water store content).
To get hot water I have to turn the heating off for a few minutes.
Even then the "hot" water is still often only warmish.

I suspect(ed) the diverter valve being contaminated with sludge - any
other ideas?

TIA -
--
Frank Erskine
Does the demand light for HW come on? If so, leave a tap on for some time -
do any radiators begin to get hot? If, so, your diverter valve is jammed
(be it sludge or malfunction). If the demand light does not come on, then
you probably have a split/worn diaphragm inside your diverter valve
assembly.