We know what your wiring diagram looks like.
What we are looking for is...
Or to be clear, can we see a photo of the wiring behind and connected to your existing stat?
All you have told us so far about the existing stat and it's wiring is...
So, you have three wires on the stat, two are in use.
From this description, it doesn't sound as if you may even have a Neutral wire.
Hence our question - going on about Tuya stats may be moot, if you need a battery operated stat, because there is no neutral.
The diagram in post #25 shows the stat wiring and the whole of the system. N is there and connects back to permanent 230A N on the 3A fused spur but is not used/connected on my stat, as I said. The stat simply connects L to SL to pass through 230V when it is calling for heat.
Apologies if I am not explaining this clearly - its clear in my head!
Hence, I can't see how a photo will help as I have shown and described it exactly as is. To photo the wiring behind the stat I would need to turn off the 230V supply again which will lose all my programmer settings, and remove the stat batteries which will also lose all of its settings.
However, if I have understood correctly, I think you have given me an answer/alternative in post #27 - to use the dry contacts in the GC version as it can switch 230V? Post #18 shows the dry contacts as also being "potential free" - I am not familiar with this term. If there are no volts then by definition there can be no current flow and therefore no electrical circuit to switch on - so it must mean something else?
In the end, as long as these "potential free" "dry contacts" can take a 230V L input and switch the 3A max L output on when heat is called for then this will work for me. Hence I would end up with the following on the GC version:
N (terminal 3 on the new GC stat): connected to permanent 230V N.
L (terminal 4 on the new GC stat): connected to permanent 230V L.
Dry contact 1 (terminal 1 on the new GC stat): connected to the same as L (jumped across to terminal 4).
Dry contact 2 (terminal 2 on the new GC stat): connected to the 230V SL output.
Hence only requiring 3 wires but making 4 contacts to the stat terminals. Make sense?
