Greetings. I am wishing to replace my ancient room thermostat with a Horstmann digital 7 day type. My old thermostat has four wires, earth, plus a red, yellow and a blue. The Horstmann unit is looking for two connections although it has three connections available, NO, NC, COM. Can someone tell me how I should proceed?

Cheers.
John.

In an earlier contribution to this discussion,
Biggooner wrote:

Greetings. I am wishing to replace my ancient room thermostat with a
Horstmann digital 7 day type. My old thermostat has four wires, earth,
plus a red, yellow and a blue. The Horstmann unit is looking for two
connections although it has three connections available, NO, NC, COM.
Can someone tell me how I should proceed?

Cheers.
John.

Your new stat doesn't require an earth *or* a neutral - only a live and
switched live. You really need to check out what the other end of the cable
connects to - but it's a reasonable bet that you need to connect red to COM
and yellow to NC - with nothing being connected to NO. [The NO contact is
only used when you're controlling a *cooling* rather than heating system].

Make sure the unused (blue and earth) cores are well insulated and secured
out of the way.
--
Cheers,
Set Square
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Thanks Set Square!