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 -