So, I have purchased a SONOFF TH10 wanting to use it to replace my wall mounted thermostat.

The thermostat has 2 connections: Always-Live and Switched-Live (which is activated of course by the position of the temperature dial in relation to the room temperature). This then returns to the central heating control.

The SONOFF however, has a Live-in, a Switched Live-out, Earth and and also needs a Neutral mains connection (I assume for its own internal power.) It also has a temperature sensor input.

So, in order for me to use the SONOFF to replace my wall thermostat, I need to run the following connections:

  • Neutral cable from mains supply to the SONOFF
  • Earth cable from mains supply to the SONOFF
  • Thermostat Always-Live -> SONOFF Live-in
  • Thermostat Switched-Live -> SONOFF Switched Live-out

In principle, is this the correct way to wire it, folks...?

I am happy with mains cabling, and I fully understand the dangers of 240V mains wiring, but I have also learned it is never a bad idea to seek confirmation from others.

Many thanks.


Looking at how the SONOFF TH10 is supposed to be used:

enter image description here

And also looking at the photos of the PCB here.

I come to the conclusion that the switched output of the SONOFF TH10 is NOT isolated from the mains.

That means that you cannot use the SONOFF TH10 as a mains isolated switch at all.

The SONOFF TH10 draws its power from the mains directly. That then also connects mains to the switching output. If you would use that as a replacement for your wall mounted thermostat you must be 100% sure that that is allowed and safe.

I am 100% sure that that will not be safe. All the wall thermostats I have seen use a low voltage and mains isolated connection from the central heating unit to the thermostat. This has the advantage that safety isn't an issue, also thin low-voltage wires can be used.

Only if your current wall thermostat is of a type that directly switches mains voltage would I say it is OK and safe to use the SONOFF TH10.

If that is not the case then using the SONOFF TH10 as a wall thermostat replacement will very likely result in an unsafe situation. In the heating system in my home, if I would do this and it would work (nothing blows up) then next time a mechanic does maintenance on my heater, (s)he might get an electric shock. That's not a risk I would take.

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  • \$\begingroup\$ Appreciate the advice, @Bimpperlrekkie, thank you. The existing thermostat I have does directly switch 240V mains. One cable is permanent live, and the other cable is the switched live. So, with this identified, I think this would be safe to wire the SONOFF. \$\endgroup\$ – John Feb 15 '19 at 9:18

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