-
I wouldn't place any faith in the colours. Central heating engineers do all sorts of random things.
What is the old thermostat and what wire is connected to what on that?
Most (all?) UK[1] mechanical thermostats are a change over switch so you have common, normally open and normally closed. You should be able to disconnect it and then measure with a multi-meter to work out what is what.
In the case of the DT90 connector A is common, B normally open and C normally closed. A connects to live (or your external timer if you have one of those) and then B and/or C to your boiler. If you get B and C the wrong way round the heating will come on when it is hot instead of cold rather than the other way round.
[1] The US seem to do it differently with 24V control circuits and extra settings for turning on your cooling
You are reading a single comment by @jellybaby and its replies.
Click here to read the full conversation.
jellybaby
Tomo187
Thermostat question:
I have an old mechanical Honeywell room thermostat and I would like to replace with a new digital one but there seems to be many wiring types.
Currently I have red/blue/yellow/yellow-green. I've done a little research and understand what they are and what they're doing but don't know what a replacement needs. There seems to be a few options out there.
Any help as to what I can easily replace it with would be greatly received.