Controlling Immersion Heater – Part 2

The first step was to add some additional sockets and a dedicated spur for the central heating.

Checking the load on the 16A supply:IMG_0644

Shower pump – 500w
Central heating pump/boiler – less than 100w
Network switch, other adaptors – 120w
Immersion heater – 3,000w

Total: 3,720w = 15.5A – so the supply is sufficient, and it would be rare that all devices are on full load at any one time.

Today I added an additional double socket and fused spur, and re-configured the layout.

enclosureAn Idratek QRH Din module fitted perfectly in a Gewiss GW40102 enclosure. The new immersion heater cable goes into the enclosure from the fused spur, only the live cable is cut and connects to the relay contacts (output 4), and then feeds the immersion heater.

The pink cable (mains rated) connects the module to the Idratek network.

I have also added a five-core cable to relay outputs 1 and 2 to control the central heating (hot water and heating), and a two-core cable to one of the inputs to sense when the hot water pipe is getting hot (and therefore the boiler is working).

The finished enclosure looks tidy:



Controlling Immersion Heater – Part 1

2015-06-27 10.43.27There 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).