I'd first be checking out and probably changing the full diverter valve. Usually the finer points of whats wrong become apparent when a decent engineer has the boiler in front of him.
The DV in the Ravenheat
is almost the same as that in a Worcester + a load of other boilers
so there is no logical reason that some have a phobia about Ravenheats apart from the fact that they have been selling them in BNFNQ as a DIY item.
A common attitude seems to be :- "If DIYers fit them and do us out of work then they can fix them as well."
The difficult part for you is to find someone like Tony or myself who are happy to move into the niche that has been created.
If you ring Ravenheat on 0113 252 7007 then tell a white lie by pressing #2 they should be able to recommend a local engineer if you explain the situation. [It was the case that the people on the end of the line when you press#1 were not aware of their approved installers list. Perhaps that has changed now.]
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