Does anymone know an "instantaneous water heater", that can be controlled via Home Assistant?


the amount of electricity consumers grows constantly in my home. We try to avoid any local burning of climate damaging gas or oil (Clearly we have to “hope”, that the overall generation of electricity will be 100 % CO2-neutral in a near future).

We have this type of consumers:

  • Normal electrical houshold-consumers (washing maschine, dishing machine, TV ans so on)
  • Heat pump for heating the rooms
  • Electrical car
  • Instantaneous water heater (Durchlauferhitzer) for warm water (e.g. shower)

At some point in time, all the consumers are on at the same time. Then, the power, that my house consumes is getting very big.

Especially the Instantaneous water heater needs a high amount of electrical power, for quite a short time. This time is also not very good predictable, because the people can take a shower at every time of the day.

For the other consumers, this usage time can be managed.

I want to be able to stop the Heat pump and the charging of the Electrical car, when the Instantaneous water heater starts.

Therefore I need an instantaneous water heater, that gives me a signal (via MQTT?) when it starts up. Then I could set up an automation and pause the heat pump and the charging of the Electrical car while someone is having a shower. This would limit the power usage of my house, based on rules.

Does anyone know, which Instantaneous water heater can give me such a signal? Or that can give more signals, e.g. the current power, the used energy and so on?

Most of these heaters have dry contacts:

One for a slave device: if the heater is heating the slave device is switched off
One from a master device: if the master is in the heater stays off.
You could connect these devices to any device which has IO, eg Sonoff, esp8266/32, door sensors (replace the reed switch).
Which model do you have?

Ok, thanks for your answer @JeeCee .

I have got a [Clage DSX Touch]. I will check the manual, if I have those dry contacts.

Well maybe you can use a SONOFF POW switch with your electric heater; it also shows power usage and consumption. Then you can use an automation like “if Sonoff Pow power usage goes above 20W; then turn off heat pump andcra charge”…

A sonoff doesn’t handle 21 kW (21000W!) very well… :fire: and doesn’t support 3 Phase.

If you don’t have those contacts you could use a relay (“contactor”) and control that with either a sonoff or an ESP.

I have just read again deeply into the Clage DSX Touch. In the device is the CLAGE Homeserver HSX firmly integrated. This has a REST-API that can be used with simple HTTP(S)-GET commands via WLAN. Additional accessories are NOT required.

The device uses WLAN. If you have registered in WLAN, a JSON file comes as a response to an HTTPS query. In the app store, there is a mobile app that connects to this (CLAGE Smart Control). With suitable means, you can also watch it communicate (with a packet sniffer). This is ordinary REST. Any PUT, POST, GET queries and back comes a JSON. The app has the default user and the default password in it (Security?). The start page works without.

That would be a way. One could create an integration for it. But, I can’t poll the REST API all the time. I will look if there are ways to set a hook, e.g. to the current power state and then have a trigger on this sensor.

But I would have to reverse engineer the api and the manufacturer can change the API at any time and then the integration would break again.

Of course it would be better to have a device that offers something like that officially directly from the manufacturer.

Exactly that is my problem. The electrical curcuit ist the domain of the electrical service company. I do not want to change there anything. I do not want to loose any warranty or break official rules.

Clamp meter that talks to home assistant on the water heater would be my suggestion. Then just use the clamp meter status to switch off the car etc.

Yeah I was also thinking a clamp meter….

This is a great post about an energy management system mit HA:

It does not works with an instantaneous water heater but with a huge storage for warm water.

I have meanwhile reverse enginieered the REST API of my Clage Homeserver. The actual status of my research is published as Swagger API documentation.

The API is not documented by Clage, I have tried to figure out the functions by “try”.

But the actual problem is not solved by the REST API. I can “only” poll the API at specific points in time, so I cannot retrieve a real time trigger of the electrical load of the device.

I have then changed the concept and retrieve now the overall load of the house from a meter, that was includes in my Solar Edge PV system via modbus. But Modbus is also a Pull-based system, it just can be quite fast (1 pull per second).