thanks for your quick reply.
Sorry your right, light isn’t the best.
I have the following connections in the existing T40:
1. Yellow and Green to earth
2. Grey to number 2.
3. Black to number 3
4. Brown to number 1.
Spot on with the T4.
So yellow and green not needed.
I’m trying to update my old manual Honeywell T40 thermostat to a programmable T40 on a combi boiler.
the man in the shop said nice easy swap but once I removed old I found there’s too many wires.
I think the T4 only needs 2 but the old T40 has 4.
Is it a simple problem to solve or do I...