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

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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
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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.
 
As already said you simply put the blue in a block connector or something else to stop it connecting to anything.

As to "Smart" thermostat, it is all down to boiler type and rest of the controls. Not used the type you have, but have used Nest which is also classed as "Smart" and in the case of Nest it connects to Energenie TRV heads.

With an oil boiler they in the main switch off/on, so the "Smart" thermostat has to include some form of anti hysteresis software, so as it approaches the target temperature it starts using a mark/space ratio (switching off/on with varying lengths of off and on) to ensure the boiler does not over shoot the target temperature.

However today most gas boilers are modulating, that is the output can vary, switching the boiler off/on can upset the whole idea of the modulating boiler, Hive have found a way around the problem with its "heat on demand" so the TRV tells the thermostat it wants heat, so the thermostat runs for 1/2 hour, so the thermostat is more like a hub then a thermostat, as with any modulating boiler the TRV head controls the temperature in each room.

Nest uses OpenTherm connected direct to boilers ebus and the TRV near the Nest thermostat are linked to the thermostat using a follow command.

EvoHome and Tado again the thermostat is more like a hub, and it controls boiler by reading the info sent from the TRV heads.

Netatmo I see do a TRV head to go with the wall thermostat, however I can't find out how they interconnect, as with my cheap electronic thermostats it has functions like open window detect, which in my case is more about open door detect so it auto turns off heating in kitchen when we have the door open unloading shopping.

But I will guess in some way the wall thermostat and the TRV head interconnect, clearly a TRV head can open up as much as it wants but the radiator will only get warm if the boiler is running, so the "Smart" thing is how the two are linked. To my mind Nest is rather poor, and EvoHome very good, but the design of the house also matters.

The old house we had was open plan, and a wall thermostat in centre of the house controlled all ground floor rooms, and TRV's just stopped bedrooms getting too hot, my mothers house had doors on the rooms so each room independent and so electronic TRV heads used down stairs. However no link to thermostat in hall, the only thing the thermostat did was turn off the heating in warm weather stopping the boiler from cycling. And this house unlike other two uses oil not gas, so only way to control boiler is switch it off/on. Mothers house boiler would modulate due to return water temperature.

So mothers old house we controlled the TRV heads with the phone, and they in turn controlled the boiler with the return water temperature, this house we control the wall thermostat with the phone, and the wall thermostat in turn controls the electronic TRV heads, we can also directly control the heads so can turn dinning room down after evening meal, but in the main simply control wall thermostat.

As to if the wall thermostat and TRV heads need some form of link, not so sure, however clearly if you want to alter temperature using geofencing then the TRV and wall thermostat must be linked, but using simple times, you could set both independently to work at the same time.

Your thermostat is likely A1 with a non modulating boiler, i.e. oil or very old gas boiler, but not so sure with modern gas boiler? As to why manufacturers make it so hard to find out how there products work I don't know, with mine for example using the phone or tablet app, I can see all TRV heads and wall thermostat current and target temperatures, but on the PC have to use a web page and have different tabs for wall thermostat and TRV heads, I have to use a different app on phone to control room temperatures to domestic water, and you only find it all out when you come to use it.

Tried geofencing with TRV heads, found the built in anti hysteresis software results in it taking 3 hours to reach target temperature, and I simply am never far enough away from home to use it.

So I never alter the central heating with phone, however I do switch on the AC with the phone, I will manually switch it on when an hour from home on hot days. It is simply a plug in adaptor, however I still use the TRV heads to see how hot the room is so I know if AC is required.

Would be nice to get a report on how your system works, so others know if Netatmo is any good.
 
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