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Discuss Replacing 3 wired thermostat with 2 wired digital thermostat in the Central Heating Systems area at ElectriciansForums.net

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A 3 wired thermostat is being replaced with a 2 wired digital thermostat powered by batteries. Is it necessary to know how the 3 wired thermostat is connected to the boiler before replacing the thermostat? I have attached images of the 3 wired thermostat and its wiring diagram.
 

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Sintra

Admin
Supporter
If it’s a 2 wire stat then just use red and yellow and put a connector block or wago on the blue.
 

Sintra

Admin
Supporter
Are you going from 3 wire 230v to 2 wire 12v?

I think I’d rather disconnect blue at each end.
If he is then the connection at the boiler will be wrong :)
 
  • Thread Starter Thread Starter
  • #7
Are you going from 3 wire 230v to 2 wire 12v?

I think I’d rather disconnect blue at each end.
The instructions with the digital thermostat say "If there are only two wires they are the control wires -if there are more than two wires, identify the two control wires. They are usually black or grey.
Note: If there are more than two wires, the others are power supply wires and are useless here. They are usually brown, blue, green or yellow. "
 

Paignton pete

-
Arms
Esteemed
In answer to your first question. Yes I would like to know how it is connected to the boiler. And I would like to see installation instructions for new thermostat.

Some boilers do not have a permanent live and work off a switched live and neutral only.

There are lots of ways to wire in a boiler.
 
  • Thread Starter Thread Starter
  • #9
In answer to your first question. Yes I would like to know how it is connected to the boiler. And I would like to see installation instructions for new thermostat.

Some boilers do not have a permanent live and work off a switched live and neutral only.

There are lots of ways to wire in a boiler.
Thanks. The installation instructions for the digital thermostat are as my previous post, there are no instructions for the boiler. It would appear to be a matter of isolating the control wires from the old thermostat and using them in the 2 wired thermostat.
 

Paignton pete

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Arms
Esteemed
Without knowing all the facts I would not proceed. I would want to see the actual wiring in the boiler to get the full picture before doing anything with stat.

I would not ask anyone to remove the cover of a boiler to get access to wiring unless they know what they are doing.

It may be a case of blanking of the blue as has been said, but would want to prove this with testing and inspection prior to installation.
 
  • Thread Starter Thread Starter
  • #11
Without knowing all the facts I would not proceed. I would want to see the actual wiring in the boiler to get the full picture before doing anything with stat.

I would not ask anyone to remove the cover of a boiler to get access to wiring unless they know what they are doing.

It may be a case of blanking of the blue as has been said, but would want to prove this with testing and inspection prior to installation.
Ok. Thanks again.
 
In this case put the N safely in a connector and just use other two connectors.

I would agree that having just two wires to the thermostat does not mean it works on 230, or 24 volt it could be a variable voltage connected to the OpenTherm terminals with some thing like the Nest e, but that is not the case here.
 
  • Thread Starter Thread Starter
  • #13
In this case put the N safely in a connector and just use other two connectors.

I would agree that having just two wires to the thermostat does not mean it works on 230, or 24 volt it could be a variable voltage connected to the OpenTherm terminals with some thing like the Nest e, but that is not the case here.
It's actually a Netatmo digital thermostat- 2 wires.
 
  • Thread Starter Thread Starter
  • #15
So digital means it turns off/on, and analogue means it turns up/down? Or does digital refer to the display and have nothing to do with the thermostat?
Netatmo don't use the word digital, that's me for the display. Netatmo call it a smart thermostat because it can be used via wi-fi or hardwired.
 
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