Have a look underneath at the diverter valve arm and see if it moves across for heating and then back to rest in hot water....I would guess not and it is sticking in heating
The diverter valve powers over to the ch position and rests in dhw mode so i cant see it sticking in the ch pos but it poss ,can you see the lever on the side of the valve move after a ch demand (takes 12 seconds). if the ch is off and you turn a hot tap on does it fire up.
Yeap, diverter valve sounds stuck, did one on thursday gone actually Remember to fully drain down sysytem and cover the pcb box with a plastic bag and a towel (Tip) + turn off electrics as well. Failing that, get a guy who knows and works on them.....
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