Fitting NEST

[stem]

OK Heatlink and nest installed and working. Ended up replacing the timer with heatlink.

Good, that's the proper way to do it.

Original dial thermo is still there too. I guess I need to remove this.

You can't just remove it, otherwise the heating will remain 'open circuit' and never come on. So, the old wired thermostat needs to be 'decommissioned' properly. You can do this in 3 ways.

1. Find the opposite end of the thermostat cable to the thermostat, and disconnect it. Then link the terminals where the two switching wires (but not any neutral, if one is present) came from together.

2. Remove the existing thermostat and replace it with a junction box, connect the two switching wires together and isolate / insulate the neutral (if there is one)

3. Leave the existing room thermostat in place and put the switching wires in the same terminal.

No 1 is the best option if possible, as the redundant wiring to the old thermostat can then be removed, and if practical, used to provide power to the Nest thermostat from the Heatlink. However, usually the existing wiring runs from the thermostat to the wiring centre and not the programmer so can be more trouble to move than it's worth. So, most people either run a new 12v cable between the Heatlink and Nest Thermostat T1 & T2 terminals or use a separate plug in power supply for the thermostat. IFAIK both methods use the wifi for comms.

 

[paulfoel]

Good, that's the proper way to do it.


You can't just remove it, otherwise the heating will remain 'open circuit' and never come on. So, the old wired thermostat needs to be 'decommissioned' properly. You can do this in 3 ways.

1. Find the opposite end of the thermostat cable to the thermostat, and disconnect it. Then link the terminals where the two switching wires (but not any neutral, if one is present) came from together.

2. Remove the existing thermostat and replace it with a junction box, connect the two switching wires together and isolate / insulate the neutral (if there is one)

3. Leave the existing room thermostat in place and put the switching wires in the same terminal.

No 1 is the best option if possible, as the redundant wiring to the old thermostat can then be removed, and if practical, used to provide power to the Nest thermostat from the Heatlink. However, usually the existing wiring runs from the thermostat to the wiring centre and not the programmer so can be more trouble to move than it's worth. So, most people either run a new 12v cable between the Heatlink and Nest Thermostat T1 & T2 terminals or use a separate plug in power supply for the thermostat. IFAIK both methods use the wifi for comms.

Thanks. Yes I understand. Noticed if I set the exisiting low it overrides nest - as it should.

Was hoping I could just use existing power but I guess not. Not possible to run wire from heatlink to nest thermostat - too far.

 

[paulfoel]

OK so I've got an existing three wire thermostat. Nest docs are a bit unclear - can I use these wires to power nest?

 

[Dan Robinson]

What you going to switch the boiler with?

 

[stem]

OK so I've got an existing three wire thermostat. Nest docs are a bit unclear - can I use these wires to power nest?

By "power the Nest" because you said earlier that the Heatlink is up and running, I assume you are referring to powering the Nest Thermostat and not the Nest Heatlink. If so, I have explained this already.

No 1 is the best option if possible, as the redundant wiring to the old thermostat can then be removed, and if practical, used to provide power to the Nest thermostat from the Heatlink. However, usually the existing wiring runs from the thermostat to the wiring centre and not the programmer so can be more trouble to move than it's worth. So, most people either run a new 12v cable between the Heatlink and Nest Thermostat T1 & T2 terminals or use a separate plug in power supply for the thermostat.

 

[paulfoel]

By "power the Nest" because you said earlier that the Heatlink is up and running, I assume you are referring to powering the Nest Thermostat and not the Nest Heatlink. If so, I have explained this already.

Yes I meant thermostat.

 

[dave1w]

When I fitted my NEST, I put the heat link where the original danfoss timer thing was and wired it in. What I found was that the wires from my thermostat in the living room ran to the original timer, so I replaced the old thermostat on the wall with the NEST, and connected the other end of the wires into the heatlink at T1/T2. This powers the thermostat and also lets it communicate directly with the heat link.

You would need to work out two of the three wires you have at the existing thermostat and where they come to supposedly at the old timer. I am presuming that the timer is / was in the same place you put the heat link?

Does that make sense?

 

[dave1w]

Just to add, make sure you disconnect the other end before attaching to the NEST thermostat as I think your original thermostat was a 240V one?

just found this - https://nest.com/support/article/Learn-more-about-identifying-thermostat-wires - may help

 

[paulfoel]

When I fitted my NEST, I put the heat link where the original danfoss timer thing was and wired it in. What I found was that the wires from my thermostat in the living room ran to the original timer, so I replaced the old thermostat on the wall with the NEST, and connected the other end of the wires into the heatlink at T1/T2. This powers the thermostat and also lets it communicate directly with the heat link.

You would need to work out two of the three wires you have at the existing thermostat and where they come to supposedly at the old timer. I am presuming that the timer is / was in the same place you put the heat link?

Does that make sense?

Yes similar to me. Heatlink has replaced the original timer (in the kitchen). Nest thermo is currently sitting in living room USB powered.
Old thermostat is still there above it (set to high to allow nest to do its stuff - I noticed if I set it low it stops nest raising the temparature).

So yes thats what I thought you could do - replace original timer and use existing wires to both power nest (so no need for usb) and also communicate with heatlink. Communication is not really an issue because its working at the moment wirelessly but it would be nice to get rid of old thermostat and usb cable.

Question is how do I know where thermo wires go to?

 

[dave1w]

If you replaced the timer, maybe the thermostat is wired in between the heat link and the boiler now? Maybe trace the CH wire from the heat link to the the boiler and see if anything if wired into it.

 

[paulfoel]

One other thing I was thinking of. The nest thermo has a battery doesnt it? How long does it last if not powered and does it warn you?

Wondering if I could additionally power it using a battery pack (like the one for phones). Would imagine the draw is small so it would last a while.

Trying to see how I could get away with trailing usb cable...

 

[stem]

Question is how do I know where thermo wires go to?

Usually the thermostat cable comes from the wiring centre which most often, is found near the hot water cylinder, and close to the motorised valve. One of the wires from it will be connected to the white wire going to the motorised valve. Once you have identified the cable it should be electrically tested to confirm. This is because not all installers choose to run their cables in the same manner.