Perhaps not as bad as it first appears. The instructions you posted #17 does say it has both internal and external sensors, so you would need the 'internal' one. See if it makes clear how to switch to this. The actual wiring is tricky, tho', since it isn't 100% clear (actually, not even 50%...) how terminals 1,2,3 and 4 are wired internally. 3 and 4 are simple enough - that's N and L (which you currently don't appear to have). Then there's how to connect to the 'switching' terminal, the one that'll turn your boiler on and off. The diagrams are contrary. Post #3 suggests that 1 and 2 are an isolated switch, but the later diagrams #18 suggests a live feed to 1 or 2 internally. Sorry, I'm stumped.
The contacts are volt free. Separate to the L&N. He hasn’t got an N. That’s the challenge for him, or send it back to AliBaba, or wherever it came from.
The diagrams in #18 are for three different models GA GB and GC. post 3 would seem to be what we are looking at. But hey, they all need a neutral.
That's what confuses me - 1 and 2 do seem to be volt-free, not connected to anything else. And yet diagram GA seems weird based on this.
Steven, you have two choices; (1) get a sparky to run a new wire from the wiring centre/boiler to the room stat location - this should be 3-core + earth, or (2) get a new stat that's battery operated. Or refit your old one...