hot water does not always come on, whether it is set on central heating or hotwater only. you have to have tap fully open before any hot water appears( this is a waste given the current water shotage) no fault shows up on display, I have had local ch engineer to look at problem but they have not come up with a fixe as yet
From your diagnosis it sounds like there is a probelm with the differential valve. This is a 3" circular brass componant that is attached to a 3 way valve on the bottom left of the boiler. Refer to the Manufacturers insrtuctions. It could be a small split in the diaphram. Worth having it checked by a qualified engineer.
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