Danfloss TPOne-M wiring

[tobyj]

I want to replace an old rotary thermostat with a programmable Danfoss unit. I figured (maybe wrongly) a thermostat for old boilers is going to be little more than a glorified switch, so the wiring would be easy. But having pulled off the old one, I'm confused.

The old one has 3 wires: brown (wired to 'L'), blue (wired to 'N') and yellow/green (wired to earth symbol).

The Danfloss unit looks like this:

My inclinations are that I should be putting brown to NO1 and blue to COM, and yellow/green to nowhere, but my suspicion is that there's maybe no power to the thermostat itself in that configuration, and it aint gonna work (it has no battery). I don't really like the 'try it and see' approach to wiring when there's a mains current involved also, so if anybody has any advice that'd be great. Possibly this unit just isn't compatible with my boiler, but also just as likely is I've not understood.

 

[Deleted member 267285]

I’d say more likely that the existing wiring is brown to live and blue to switched live, earth to earth. Post a photo if you can of existing wiring.

 

[tobyj]

Sure... Old thermostat looks like this:

And wiring diagram on the case:

 

[Deleted member 267285]

As I suspected, live and switched live. For the Danfoss you’d need additional wires. You could opt for a battery type, or wireless type?

 

[tobyj]

Thanks - so looks like I should have got the TP-One-B, which looks like it would work with the wires I've got coming from the boiler?
Presumably brown --> COM, blue --> NO and green/yellow --> NC

 

[stem]

Thanks - so looks like I should have got the TP-One-B, which looks like it would work with the wires I've got coming from the boiler?
Presumably brown --> COM, blue --> NO

As the TP-One-B is battery operated, then yes it doesn't need a neutral connection, and the wire connections you describe to COM and NO are all that is needed.

and green/yellow --> NC

No! You should not connect anything at all to NC, especially an earth wire. If you did, when the thermostat is in the off position you will create a short circuit between live and earth. At best you will blow a fuse, at worst damage the boiler or new thermostat.

The original Danfoss unit that you posted the wiring schematic for is designed to replace an existing programmer and provides both heating and hot water time control, plus a room thermostat remote sensor for the central heating. So if you have an existing programmer somewhere you may still be able to use it.

The TP-One-B is a programmable room thermostat. If it replaces the room thermostat any existing heating time control would need to be set to be permanently 'on' 24/7.

 

[tobyj]

Brilliant - thanks for your help.