Replacing old Siemens thermostat with Honeywell THR870C

[Adam42]

I currently have a Siemens RWB29 Programmer attached to my boiler. There is also a Siemens rotary dial room thermostat which isn't working very well. I have got myself a Honeywell THR870C to replace it. Unfortunately I'm having trouble working out what the wiring should be.

The THR870C manual has 8 different wiring diagrams in it, none of which seem to say they are for replacing an existing room thermostat.

The Siemens RWB29 manual doesn't have much information either.

Is it possible to use that THR870C as a replacement for my current thermostat? If so how do I wire it up?

 

[Adam42]

Here's some pictures of the current setup.

After talking to a friend, the thought was that the brown wire is live and should therefore be connected to 'A' on the THR870C and the black wire that's attached to terminal 2 currently should go to 'B' on the THR870C.

If that's right the loose black wire, and the green and yellow earth wire won't be needed with the new setup.

I'm planning on giving that a check with a voltmeter tomorrow to make sure, but I thought I'd also ask here to see if anyone has any other thoughts on it.

THR870C

• Adam42
• 12 Nov 2013
• 1

Thermostat Exterior

• Adam42
• 12 Nov 2013
• 1

Thermostat Interior

• Adam42
• 12 Nov 2013
• 1

Thermostat Wiring Detail

• Adam42
• 12 Nov 2013
• 1