There was one double socket and one fused spur (for the immersion heater) in the airing cupboard, but of course this was used to supply various other devices including a network switch, shower pump, and even the supply for the central heating, etc. The circuit is supplied via 2.5mm cable and a 16A MCB on a radial circuit.
My problem was what to do when the boiler failed to heat water ready for the morning. Although a rare occurrence, the first anyone would know about it would be no hot water for a shower or bath. Fortunately we have an immersion heater, but that can take nearly an hour to heat a tank of water, and it’s also not very convenient getting to the switch in the early hours of the morning without waking anyone up.
As Idratek is now cabled around the house, it seemed a sensible solution to control the immersion heater if a problem arose with the boiler.
The plan is therefore to sense whether hot water is being provided by the boiler within a certain amount of time from the controlled time, and switch on the immersion heater if there is a problem (and of course notify of the problem).