I have a Drayton mechanical room thermostat and I want to replace it
with a programmable digital thermostat.
The Drayton had three wires connected to its three terminals numbered
My CH system has a boiler indirect I think a HW CH programmer and a
three port motorised valve that seems to be controlled by the room
thermostat. the problem is that the Drayton seems to have seized up
and will not cut off the heating . that's why i want to replace it.
The new one I've bought has also three holes named NO,COM,NC.
What wires do i connect to what terminal?
I do know that the voltage between 1 and 3 is 230 V and also between
2and 3 is also 230 V.
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!
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