"DavidB" wrote in message
news

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


--
DavidB

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.