Immersion heater 'smart' switch - recommendations?

I would like to control my 3kW immersion heater from a computer program ( Does anyone have any recommendations for good quality high load smart switches with open interfaces please?

Here’s a roundup of the ones I have found:

Sonoff POW R2. Cheap and cheerful, and it can be flashed with Tasmota. However, this Sonoff device has shocking poor safety reviews on Amazon!

Another contender is Optimum OP-BM, a WiFi immersion controller - which looks a lot more sturdy! It appears to be controlled via a Chinese cloud service Tuya, but at least it has an API for automation.

Timeguard sell a similar device. However it is apparently proprietary and uses a closed control system.

Next, we have Energenie MiHome 3kW relay, or Aeotec ZWA006 ZWave controller. However they are both expensive, and then require the extra cost of a hub.

For completeness, another option: VIBIRIT 16A

And finally, the various Solar Immersion Diverters, iBoost+ or Solic or Eddi. All of which are very expensive and none of which have WiFi or an API, AFAICT.

Any experience from the emon community would be appreciated.

I forgot to mention your very own Control Relay. Which looks exactly what I am looking for but I can’t find in the shop anymore… Is it discontinued or other issue? WiFi MQTT Relay / Thermostat - Shop | OpenEnergyMonitor <<< broken link

Have you seen the responses to your other thread - on ALMOST the same topic?

Have you looked here: Learn→PV Diversion→Introduction ?

You can buy a hardware kit for Robin Emley’s Mk2 PV Diverter from his website You don’t need to use the measuring side, and the software for that is published there - so it’s completely free, both in accessibility and in cost - and you can modify it to accept control input, which is likely to be a digital input, serial or radio, from whatever you wish however you wish, subject of course to the limitations of the kit.

Or you could build your own, maybe with an Ethernet or Wi-Fi equipped Arduino and a commercial solid-state relay. If you do go down this route, make sure you get the SSR from a reputable supplier, as there are dangerous clones on sale.

Most ‘smart’ switches will not safely switch a 3kW load.

I am going to use a 25A contactor switched by a Sonoff Basic flashed with Tasmota to control the switching hooked up to

Just need to find a suitable enclosure.

Getting a contactor that is NO (Normally Open) if the switching fails it will fall back to being off.

Beware, depending where you put the switching it may fall under Part P of Building Control regs in the UK.


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Thanks for the info folks. I am not afraid of building my own but would prefer to buy, and am also worried about burning down my house. Still looking for a manufactured option which is sturdy, reliable, and safe.

May I ask what happened to Emon’s own MQTT Control Relay please? It is no longer listed in the shop.

I don’t know, but I think @Gwil might.

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Just checked with @glyn.hudson, the WiFi relay is out of stock, but we should have more in a weeks time. The product item should be back shortly, not sure why its disappeared

Thanks, the shop link is working again, and I’ve just ordered one!

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Thanks @butako1!

Thanks! Yes, we should have more stock of the WiFi relay in about 1 weeks time: