Replacing Room Thermostat

[DavidB]

Hi, I have a honeywell T40 thermostat which i want to replace with

programmable one. However on the new stat i only have 3 terminals:

COM NO NC

On my old one I have 6 and 4 of them are in use:

1= Red 2= Blue 3= Yellow 4= Earth

Any idea which wire i put in what terminal on the new stat Unfortunately the old stat i numbered not letters?

Any help greatly appreciated. Thank

-- DavidB

[john]

You have the same with the new one - but you are not counting the earth - perhaps it is double insulated and doesn't need it - or is it a separate tag?

If you examine the old one there may be an indication (maybe a diagram) of the contact arrangement. Alternatively test it with a circuit tester. NO and NC should never connect. COM to NO should make a circuit what the temp is turned up to above ambient. You may find it worth looking at the boiler end to deduce what is what. There may even be a diagram. Convention would be to connect the red to the COM.