Basic wifi controlled switch for immersion heater

Sorry in advance for the basic question and apologies if this has been covered before.

We are in the process of installing Rointe wifi-enabled radiators in a holiday rental property. I can control these with the Rointe Connect website/app. Plus, with help from another topic on this forum, I am able to control the radiators programmatically, by hitting the Rointe Connect web services.

I’d like to do the same thing with the hot water. This is currently a single cylinder with immersion heater on a wall switch - it’s either off or on. Am not really interested in knowing the temperature, just turning it on and off on a schedule, or off completely when the house is unoccupied.

Rointe have an immersion heater with wifi integrated but it’s not very big and I’d prefer not to have to replace the existing cylinder, etc.

So my requirements are:

  • Simple wifi switch which can handle the load of an immersion heater
  • Doesn’t require punching holes in the router firewall to access (ie. talks to manufacturer’s cloud service)
  • Supports setting a schedule, ie. turn on for these hours every day
  • Supports disabling the schedule and switching off
  • Can be controlled programmatically (from outside the home, via cloud service)

Any advice and guidance appreciated!

I’m not sure I’d go so far as to recommend it for others to use, given how close to its rated load it’s working, but I’ve had a Shelly 1PM switching my 3kW immersion at least daily for well over two years now, and it hasn’t missed a beat. Ticks all of your requirement boxes.

It would need to be installed with care: small terminals and large loads are a potential recipe for problems if not done well; and you should look to take steps not to switch off the immersion whilst it’s running to avoid arcing on the tiny internal relay.

I do this by using its power monitoring to recognise when the immersion’s own thermostat has switched the element off before I switch the relay off.

@Troon, thanks for your speedy reply!

The Shelly looks pretty nifty. Am slightly concerned about your caveats given this is a holiday rental property - any solution would have to be safe and pass the electrical inspection that happens periodically, and also resilient to tenants doing silly things like flipping switches randomly.

Am I right in thinking that to control the device remotely I would have to either a) allow access through the house wifi router firewall, b) sign up to be a Shelly integrator to get access via their cloud service? It’s not completely clear from a quick look at their docs whether the HTTP API is just “in home” (hitting the device on local wifi) or cloud based.

Thanks again

I control mine via Home Assistant, which already has access through my firewall. I’ve turned all the remote cloud functions off on my device, so I can’t tell you, sorry. As I understand it, their devices talk to their server and presumably receive commands without additional firewall holes:

Are you using Home Assistant?

No I’m not using home assistant (at least not yet). It’s very simple to hit the Rointe Connect service directly with HTTP requests and get the status / send commands. I’m a developer so was just going to write a simple AWS lambda to periodically check and update the rads in case the tennants have fiddled with them, and turn them right down when the house is unoccupied. Really simple requirements!

just get any light switch, that does comply on all your other demands, except the load and let that switch control a heavy contactor. Way safer and the amount of suitable hardware gets much bigger this way.

Not sure where you are but I use a Tesla T-Smart replacement Immersion Heater thermostat, there’s a custom addon for HA too. No need to empty the cylinder, the thermostat just slides out and new one slides in and connects to existing wiring

Also, there are replacement Zigbee or WIFI controller Fused Spurs that can control 13A

Also, do a search on here, “immersion”, there a few threads

@Holdestmade, thanks for the info, these look promising. Do any of them provide an API to control from outside the home (ie. via the cloud), ideally one that’s documented? I couldn’t find info on quick scan.

The T-smart one has an app and the WIFI one is the Tuya / Smartlife app. If you integrate any of them into HA you can use remotely ?

I’m not using HA (at least not yet) and prefer not to punch holes in the home router firewall, so ideally looking for something that connects to manufacturer’s cloud and can be controlled using their API, as is the case with the Rointe radiators. But maybe I’m asking too much…

In that case, the T-smart and the WIFI one should be fine. I just assumed that as you are on Home Assistant’s forum you’d be using it