DHW Control


Domestic Hot Water Control


How much hot water you need and how to control it?

Immersion Heater

electrical dual immersion switch with neon I recall a time when the immersion was controlled by two switches, one labelled sink and the other bath.

Not very high tech, but functional compared to a single on of switch. However, both are manual only, with the only other control being the immersion element thermostat.


When we moved to our current home the immersion heater was plugged into a switched 13A socket. When yo wanted to have hot water using the immersion heater, a quick flick of the switch beside the plug, and there you go, after a couple of hours, you had a bath full of water. This solution was even simpler than the wired, two switch variety.

 24hr mech timer plug24hr mechanical timer plug - Masterplug TM24-MP

However, it was not long before we added a 24hr mechanical timer to that plug socket. The luxury of not only having timed hot water, but the ability to make use of the cheap electricity of Economy Seven. Just set the time to operate during the night rate and keep the water hot until needed by good insulation.

This arrangement lasted for several years, mainly during the summers, with the immersion taking preference to the gas boiler. To give it a rest.

If the boiler was already on the heat the radiators, in the winter, it was sensible to use that energy to heat the water as well.

The plan was to replace the plug in 24 hour mechanical timer with a more sophisticated 7 day digital timer.

7d digital timer wiredThis would have been hard wired instead of a plug. Hard wired would be higher capacity than a plug and more appropriate for an immersion heater.

The other advantage of this proposed replacement was that it was a 7 day controller as opposed to the previous 1 day. This would provide greater control and flexibility. It was also digital instead of mechanical so should have been easier to operate.


eddiThe current immersion controller is the myenergi eddi pictured. 

Read about the eddi here.








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