"Christian McArdle" wrote in message .net...
My guess is that the relay is probably a 5 minute delay timer. Probably
installed to prevent short cycling. Alternatively, the lot was wired up by a
cretin.

Could be either, don't really know much about relays and didn't
realise they could act as a delay timer. Is short cycling more likely
to be an issue with a 30kw boiler heating a ~125 litre indirect HW
cylinder?