Hi experts,
I have a question about wiring / base for the Nest Learning Gen 3. I am based in Australia.
I am self-installing the Nest and currently have a Honeywell CM907 thermostat connected to 2 x Sime Format System gas boilers. The two boilers both have 2 wire cables coming out of them in the basement. They are spliced together in the basement (in parallel) and a single 2 wire cable is routed through the walls and floor to the above mentioned thermostat.
As it is a 2 wire system, I understand one goes into Rh or Rc (its a heat only system) with the other going to W1.
Nest powers on, detects wires, shows temperature, and on reaching the set temperature, goes from orange to dark as expected.
Unfortunately, from the moment I plug the wires into the base, the circuit seems to be complete and both boilers switch on and never switch off. Whether the Nest is connected to the base or not does not matter, boilers stay on. If I pull one of the wires, boilers come off.
When Nest is connected to base and is in the "Off" state, I go into settings > technical info > power - it is showing lin @ 40mA. If the Nest is "On" the same setting shows 20mA.
I am not sure if Nest continues to send some minimal current to the boilers and they continue to run? Help please!
Boilers are these: https://sime.co.uk/wp-content/uploads/2017/05/Format-System-Installation-Servicing-Guide.pdf.
Old thermostat is this: https://www.plumbworld.co.uk/documents/honeywell-cm907-programmable-central-heating-thermostat-insta...
