Good afternoon my name is ***** ***** will assist with your query today.
Please give me a minute to look up you specific model of thermostat.
Looking at the wiring diagram here for your RMT230, both terminal 4 (blue) and 2 (red) are neutral\common, which is a strange colour coding, and would be inclined to use a multi meter to double check, that only black is your live.
When wiring a different type of thermostat such as the TP5000 you would normally look to run two pairs of cables, as I think you will run into issues otherwise.
As stated earlier the TP5000 has two sets of terminals; mains (marked by L and N) and a switched - which activate the boiler (marked 2 and 3), on the old thermostat the switch pair was terminals 1 and 2, so after checking with a multi meter you know Black is live from the boiler, I would jumper the Live (black) from the Live terminal L, to that on terminal 3 (switched live), then place the red cable in terminal 2.
Good morning do you still require assistance?
Can you send me a link to the type of screw driver as some of them arent up to the job, some measure electromagnetic field.
My suggestion would be to set the multi meter to continuity then check you have continuity across the terminals 1 and 2 of the old thermostat, activate the thermostat and check its making and braking the circuit.
The next thing to check is when you manual jumper terminals 1 and 2 together does the boiler start, and when you break them apart does the boiler stop.
Well based on the wiring diagram I have for you old one I cant see how the wires can be anything different (unless there are two versions of the same model).
What I would do is just focus on the switched terminals as mentioned above and check if you connect the wires in terminals 1 and 2 together if the boiler runs, and if you disconnect them the boiler stops, if it does this tells you everything you need to know to go with the wiring suggestion I made at the start.
Worst case if you cause a short, is you could blow the PCB as you end up pushing mains current the wrong way in a PCB, a new PCB is upwards of £150, so you really want to be sure, best case you probably just blow the fuse in the PCB.
Right so in essence your thermostat has two wires (the blue in term 4 is disconnected, at the other end so can be ignored).
With this known your setup is as per figure 5 in the manual referenced here. If the boiler is running could it be because you have the boiler set to continuous\bypass, otherwise during the boiler wouldnt be working at all as the thermostat was faulty?
We need to get in a position where we can get the boiler in a idle situation with Red and Black disconnected, so when you connect them the boiler starts, this proves everything is in place as we can then use the black and red for the switch side of the new stat (terminal 2 and 3).