Hot water kit to control immersion heater?

[Richard]

Many thanks to Howard for this info which has allowed me to integrate control of a hot water immersion heater into my evohome set up.

I have a slightly unusual set up in that my central heating radiators are fed from a dedicated oil boiler whilst my hot water is supplied completely separately via a vented/gravity fed cylinder which is heated by an Aga in winter and an immersion in summer.

The central heating is controlled by evohome and by using the above instructions I have been able to configure a separate bdr91 to trigger a relay which turns on the electric immersion when needed.

As advised I set up hot water using the guided configuration - binding a cylinder temp sensor and a bdr91 which is used to trigger a high current relay and thence the immersion heater. The problem with this is that whenever you switch on the hot water the system Not only correctly triggers the immersion bdr91 but also calls for heat from the central heating boiler Bdr91 causing the heating to fire up. Obviously evohome assumes that the hot water bdr91 is activating a valve not an immersion and that you also therefore need it to turn on the boiler to heat the water. Clearly perfectly reasonable in most set ups but it resulted in my central heating firing in the middle of summer whenever I asked for the immersion to go on.

As suggested to get around this I unbound the immersion bdr91. Doing this leaves the hot water temperature display on the evohome controller so you can still see the cylinder temp. To control the immersion I then created a new zone called “hot water” using the evohome controller as the sensor and bound the immersion bdr91 to this zone.
By setting the zone temp to 5C when I want the immersion off and 30c when I want it on I have easy control of my hot water. Obviously the system cannot switch off the immersion when the cylinder is at temp so I have to rely on the immersions integrated thermostat for that.

Guys, you just need to be aware that a central heating boiler setup and using a 'Boiler Relay' would activate each time you call for immersion heater demand if you use the hot water kit, and hence we don't recommend this configuration. The only way this 'could' work is if you setup as an S Plan system without a Boiler Relay, but this would then mean you can't change the CYCLE RATE or MINIMUM ON TIME which can be detrimental to oil boilers that require a lower cycle rate and longer minimum on time. If you want a Wi-Fi immersion heater, just use this - https://www.timeguard.com/products/time ... fused-spur

[keefaaa]

I have an electric only immersion heater (2 coil). Setup this way for next 24 months until gas boiler goes in. I use it only for hot water currently.

I believe I can save some money in the meantime by better control if configured with IFTTT and Octopus tariffs.

I see the above configurations have included some other sort of setup. What is your best suggestion for pure hot water on electric usage?

Should I use the evohome relay to trigger a higher current relay as above?