Thermostat Wiring Help

[Ben Be]

Hello,

I am hoping someone could help, I have a combi-boiler and looking to replace my RS1 thermostat with a Honeywell T4.

The current RS1 thermostat has 4 wires:
Neutral - Blue
Live - Yellow
3 / Call - Red
Earth - Yellow/Green

The new Honeywell thermostat is battery powered and only requires 2 wires A and B. Could someone explain which wire goes where, and what to do with the spare 2 wires?

Thanks a lot for your help !

 

[stem]

You don't need the blue neutral wire. Insulate & isolate it safely out of the way. Do not connect it to the T4

You don't need the green/yellow earth wire as the T4 is double insulated. Insulate & isolate it safely out of the way. Do not connect it to the T4

The yellow wire then goes to T4 A

The red wire to T4 B

It's unusual for the original installer to use the yellow for the permanent live and the red for the 'call' live, but in practice it doesn't matter. When the T4 switches 'on' terminals A & B are just connected to a switch that joins them together, so if they are transposed it doesn't effect operation.

 

[Ben Be]

Following your instructions, new thermostat is in place and the heating is working correctly.
Thanks a lot for your help Stem !

 

[stem]

Thanks for the update, it helps anyone who comes along later and finds this thread when searching for help with a project of their own.