Cold water at taps

Just had a heated towel rail fitted and plumber got great info from you prior to job. He gave me your contact details and said you were the man to ask!! We've had a problem for some months now where the water at the hot taps soon runs cold (central heating is fine). If we switch to emergency however, either just water or heating and water, we get instant hot water back to the taps. If we switch back to normal then water soon begins to run cold again. Any ideas? - Thanks.

Yep, this is usually the DHW heat sensor. Putting it on electric backup seems to kick a dying sensor into life again. Hard tell without seeing it in front of me though.

Cheers!
Mike

Thanks for that Mike. Just found original manual and going through the Button1 - Button2 checks I get and error reported on that sensor.