Volt Free MQTT Enabled Relay?

Does anyone know if such a thing exists ?

I’d like to add boiler control to my HA - I’ve checked my current wiring (I have a Horstmann H27XL Timer, which is linked to a Siemens RDH10RF Thermostat).
From what I’ve deduced, the RDH10RF uses volt free switching on the relay - the wiring for the thermostat consists of a L & N feed, then a separate live for the relay (24v - 240v) with the usual NC / NO connections for the relay.

I have seen people modding SONOFF basic to decouple the relay from the live feed, which I believe would give me what I want, but I’m not happy about doing this given safety / insurance implications of modding something so critical.

I looked at shelly but as far as I can tell they don’t have volt free switching (the relay switches the live feed) - which is a shame, as they are CE certified, so I’d be happy using those.

What i’m looking for is something preferably ESP8266 based - does such a thing exist ?

You can always use a second relay that is energised by the first. That way you can choose any type of contacts you require.
You can buy DIN mounted or encapsulated relays so they are cosmetically nice and safe and CE marked

Shelly 1 Relay, isn’t it volt free between 0 and 1?

I’ve never heard of “volt free”, but you should look at the Sonoff 4CH. It has four relays that are independent of the line voltage. I am using three to control my lawn sprinkler zones which runs in 24VAC.

Out of the box, the Sonoff is not an MQTT device. I flash all of my Sonoff devices with Tasmota.

Thanks for the replies. It made me look at the Shelly 1 again… I think I misunderstood the markings - I read I/O as one and zero (ie. On/off)
But it seems its actually In / Out… So I assume it load side of the relay is not actually connected to live by default (unlike sonoff)
Anyone confirm my thinking?

The relay of the Shelly1 is isolated from the line voltage. Here is a You Tube Video by the hookup guy of his evaluation of the Shelly1.


I modded a sonoff to make it a “dry contact” and it’s working fine, but you can also buy this sonoff:


Thanks folks, I’ve pre-ordered a Shelly 1 - so will have a tinker once that arrives, but it looks like it should fit the bill!

Which Sonoff did you modify? I’ve got a POW and would love to know if that can be modified.


I modded a sonoff basic following this. Pow should be more complex, and I think you will lose the energy meter functions.