replace a honeywell cmt907 with an aliexpress thermostat?

[doofusdog]

Hi all from New Zealand!

I need to replace our old Honeywell CMT907a with a nice wee Google compatible thermostat I got from AliExpress.

I have read the other similar threads on here. Our boiler is just heat for radiators.

So I have A B and C wires on the Honeywell, when the boiler breaker is on I have 240V AC across A and B, and a weird 200V AC across the B and C.

I can get the new thermostat to boot up on the 240 from A and B, but no matter what I do with the C, the boiler (a Firebird System 60) doesn't go.

I can't easily see the wiring at the Firebird, it all under covers.

So yes I could call a tradie but these systems are uncommon in this country, I'm an IT guy, my wife is a weird kind of electrician with an NZ registration, and my Dad is a retired electrical inspector, but we couldn't figure it out. Between us we are unlikely to fry ourselves, so don't worry about that.

I think I need to add another 240V feed to the new thermostat. That's easy. So the new thermostat has N and L in, N out an NC out and an NO out

So I put a new 240 into the N and L in, then where to put the other 3?

Thanks very much!
Craig

 

[ianmcd]

A red wire to 1 on new stat

B brown wire to 4 NO on new stat

Dont know what the blue wire is in the old stat but it is not a neutral (do you also have some kind of cooling unit ?) it would normally be used for that.
You will have to supply a Neutral to terminal 2 N in, on the new unit

Your old thermosts was battery powered and does not have a Neutral you new stat does require a Neutral