Apparently it's a
legal requirement to ventilate the compartment when the HWS is fitted. Not a problem if they're both disconnected.
However, it is a nuisance as it comes on when any
water is used, not just the HOT side of the mixer taps. I'd rather have the switch connected to the HOT flow side of the water
heater. Nevertheless, we're not going without a hot
shower on board!!
Cheers