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I currently have a Honeywell CM907 room thermostat and wish to replace it with a wireless Honeywell CM927 thermostat. To keep live simple, I am planning on placing the wireless receiver for the new thermostat where the existing CM907 is fixed, in order to reuse the existing wiring. Before I start though, I need some advice on the existing wiring.
Currently the CM907 has a live and switched live supply attached to A and B on thermostat back plate. The wire colours are brown and black.
At the boiler end (iSar HE35), the live and switched live go into terminals L1 and L2 (furthest left two cables on connector block). The wire colours are grey and black.
The first piece of advice I need is why the wire colours on the live and switched live supply change between the boiler terminals and the room thermostat? Can I just assume that they change at some junction that I cannot see in the wall?
Secondly, the CM927 needs a neutral supply along with the live and switched live. Looking at the wiring at the existing room thermostat, there is an used earth and unused grey cable. How can I test that this grey cable is a neutral?
Ultimately I want to do this work myself, but if I am not confident then rest assured that I will get a professional in. Many thanks.
Currently the CM907 has a live and switched live supply attached to A and B on thermostat back plate. The wire colours are brown and black.
At the boiler end (iSar HE35), the live and switched live go into terminals L1 and L2 (furthest left two cables on connector block). The wire colours are grey and black.
The first piece of advice I need is why the wire colours on the live and switched live supply change between the boiler terminals and the room thermostat? Can I just assume that they change at some junction that I cannot see in the wall?
Secondly, the CM927 needs a neutral supply along with the live and switched live. Looking at the wiring at the existing room thermostat, there is an used earth and unused grey cable. How can I test that this grey cable is a neutral?
Ultimately I want to do this work myself, but if I am not confident then rest assured that I will get a professional in. Many thanks.
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