Wow, there's off topic, and then there's off topic!
So based on the manual and diagrams, connection 1 should be live, 2 should be neutral, and 3 should be switched live to the boiler.
2 may not be connected in all installations - read about thermostat anticipators
With the thermostat down, no heating demand
1 – 2 = 5V
1 – 3 = 195V
2 – 3 = 250V
I'd agree that 1 & 3 appear to be swapped. If wired correctly then 1 should be at 240V, 2 at 0V, and 3 at 0V. That's not what you've got. Your numbers are consistent with 3 being live, and 1 being switched live. The overall result would be that the system would work, but the anticipator will be doing nothing but burning a small amount electricity constantly.
Simplest test iff you consider yourself competent to work on mains is to power down, disconnect the wire on terminal 3, power up, and then measure again. If the now loose tail is live, you have your answer. The most useful tool for this is a mains test screwdriver
as it'll tell you whether the terminal is live, rather than the respective voltage differences.
T6 installation manual
, T6R installation manual
The Lyric T6 wants to put the receiver box where the current thermostat is, or it could be relocated to closer to the boiler/heating wiring centre. It's then a wireless connection from the stat to the receiver on the T6R, or 2 wires required on T6.
If you know where the other end of the wires currently at your thermostat are, then I'd site the receiver box at that other end, and use two cores of your 3core+earth cable to connect it to the thermostat in the current location. Make very sure of your connections first or things will let out the magic smoke.
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