Room thermostat

I can't answer the question directly, but can give you some pointers.

NO = Normally open NC = Normally closed COM = Common

This is a changeover switch in which, at low temperatures, NC is connected to COM. When the set temperature is reached, it changes over so as to connect NO to COM instead.

For your application, you only need 2 wires:

• A live feed coming from the programmer when CH is on, and connected to COM. * A switched live, between NC and the motorised valve

Then, when the room gets up to temperature, the contacts will open, and the demand to the valve - on onwards to the boiler and pump - will be removed.

My guess is that the third wire going to the original stat is probably a Neutral - and the stat probably has a small internal heating element to increase its sensitivity. You don't need this wire in the new stat and MUST NOT connect it to the spare terminal - otherwise you'll have a dead short when the contacts change over.

The only hard bit is to work out which is which of the original 3 wires! Maybe someone here has experience of the Drayton stat and can tell you. Otherwise, you'll have to trace them to their sources and destinations with a continuity tester - with the power OFF of course!

Roger

Add in the symbol:

N/C = No Connection and can be used as a loop through terminal.

Not to be mistaken with NC = Normally Closed.