Attaching Honeywell cm907

[Deadlywonky]

Thanks to the excellent advice of this board I have bought a CM 907 Honeywell thermostat to replace the old Honeywell thermostat of uncertain provenance installed in my house. The system is currently set up with an old electromechanical timer by the boiler ( a combo unit). The timer has started to fail of late (slipping out of its settings) so I was intending to install the CM 907 to replace the functions of both by leaving the timer in manual on.

Unfortunately I have become rather confused trying to replace the old thermostat (see attached photo for the current wiring). I'd be very grateful for any assistance that can be offered As the wiring layout on the old thermostat has faded with time and I don't know how to proceed.

Many thanks in advance,

Tom

View media item 50657

 

[Hugh Jaleak]

IIRC 1 should be live input, 3 is switched live output, (energised when there is a call for heat), and 2 is neutral which I think isn't required on the CM907 so needs to be made safe. I would double check with the Honeywell wiring diagrams (on the Honeywell site) before doing anything though.

 

[denso13]

1 to A, 3 to B, and 2 in terminal block as it is not required.

 

[Deadlywonky]

Thanks guys, works like a charm. Now I just need to work out how to program it