Off Peak Problem

The Off Peak switch comes on every night but in the morning there's no hot water, either lurk warm or cold. I can use the booster to get immediate hot water. There's no buzzing noise coming out of the boiler anymore. I removed the front panel. The small digital display is showing a strange symbol, definitely not an error code. My neighbour (electrician) said he can smell a small burnt.

Having reviewed the posts on this forum, I think it is related to burned out relay. But I am unsure if I should replace the "relay" or the whole circuit board.

Any ideas? Also, do you know any reputatable repairs based in East London (E1)?

Thank you.

Does the board look ok?
If so replace the relay
Have you the book?
If not download one from Gledhill.
Mike