Change Analogue Thermostat to Moes Wifi

5 Feb 2022
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United Kingdom
Hi, I am looking to change an analogue thermostat to a digital one to control our wet under floor heating. Could someone please help me identify the correct wiring please.


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The old stat isn't one I've seen before and the diagram is slightly unusual, however there are some clues.


Terminals 1 and 2 in the new stat are a voltage free switch


As are 2 and 1 in the old stat

So based on the above it appears that:
  • Old stat 2 would correspond to new stat 1
  • Old stat 1 would correspond to new stat 2

As per the below diagram, terminal 4 is shown connected to N. So I'm a bit surprised to find that in your photo terminal 4 looks to have a brown (live?) wire in it


So the remaining connection would seem to me to be the live, maybe they are using P to mean 'Phase' which I've not seen before. But I think it would seem appropriate for a live supply from a programmer / timeswitch to be the L connection. [If the new stat incorporates both time and temperature control, any existing programmer / timeswitch would need to be set so that the heating is permanently on]

However, this is just my interpretation based on the information you have given, so shouldn't be taken as gospel. Ideally the wires should be traced to their origin to find out what is connected to the other end of them, and tested with a multimeter to make sure.

The hand written wire colours on the diagram you posted doesn't match your photo, so I assume that's another installation?
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Thanks for your help. Apologies for posting the incorrect picture of the existing wiring for the stat. I’ve tried to post the correct wiring. I also found a slightly better wiring diagram which would suggest the wires 2&4 are the live and neutral. If so would then correspond to 3 & 4 on the new stat and 1&4 to 1&2?


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Not necessarily. Terminals 1&2 in both devices are only connected to a simple voltage free on/off switch and not connected to the operating circuits of the thermostat in anyway. Terminals 1&2 would switch whatever was connected to them. Usually it will be a live as shown in the diagram, but not always. Sometimes the switch is used for other voltages and in that case connecting it to L would be a very bad idea.

However, it is most unlikely that yours isn't connected to 230V, but you shouldn't assume that it is. But whatever the voltage used, if you exchanged the wires as 1=2 and 2=1, you would be swapping the switching wires over from one device to the other like for like, so nothing would have changed from what you originally had.

The terminal A/B is shown as live supply that comes via a timeswitch or programmer. So the thermostat won't be able to turn the heating 'on' until the programmer says it can.

However, my worry is that there's still the issue that both terminal 4's are neutral.


But your terminal 4 has a brown (live??) wire in it.


It's not unusual with heating systems for blue wires and green/yellow wires to be used as live wires, but it would be very rare [don't think I've ever seen it] for a brown wire to be used as anything other than a live. Personally, I would want to check out what it is connected to at the other end to make sure it is a neutral before proceeding any further, or at least measure the voltages on each of the wires with a multimeter.
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