Nest install seems okay but not convinced it's working!

sparkymark75 · 1 Aug 2017

Some background. I've just recently moved into a new build. It has an Ideal Logic 35 Combi boiler with two heating zones and no hot water tank. It did have two Danfoss TP5000 thermostat/programmers.

What I've done is install the two Heat Links in the garage next to the boiler. These are wired to a junction box. 240v from the boiler junction box is fed to the Nest junction box and supplied to the Heat Links. The T1 and T2 12v connections from both Heat Links are fed into the Heat Link junction box, this is then fed to the boiler junction box and then down the brown and grey wires that were fed to the TP5000s to the Nest thermostats.

It's easier to explain in a diagram so here's how I've wired it up.

Everything appears to be working, the Nests aren't complaining, have power and report no errors. The Heat Links are green lit and respond to the Nests. The problem is when I ask for heat, the boiler fires up but the radiators never get warm. Does my wiring look correct? Could something be stopping the radiators from heating up because my house is warmer than the temperature I've got the Nests set to? Even if I push the button on the Heat Links, no heat yet everything seems to fire up okay.

EDIT: Updated diagram

Johnmdc · 1 Aug 2017

You shouldn't have the two nests connected together like you have. Each one should be connected to it's own T1 and T2 terminals on the correct heat link.
As with any thermostat you need to set the temperature higher than the ambient temperature for it to heat up.

sparkymark75 · 1 Aug 2017

Johnmdc said:
You shouldn't have the two nests connected together like you have. Each one should be connected to it's own T1 and T2 terminals on the correct heat link.
As with any thermostat you need to set the temperature higher than the ambient temperature for it to heat up.

Thanks for replying. I was confused about what you meant at first but I think my diagram isn't clear enough. The Heat Links feed their own T1 and T2 into the Heat Link junction box. This is then merged so a single T1 and T2 goes from there to the Boiler junction box. From there it splits out again so each Nest gets its own T1 and T2 12v supply.

FurstyFerret · 1 Aug 2017

Thanks for replying.From there it splits out again so each Nest gets its own T1 and T2 12v supply.

You can't - shouldn't - do that. The Nest T1/T2 terminals are not designed to be paralleled with another Heatlink. I'm surprised that it worked at all, frankly, and you're lucky you haven't broken the Heatlinks / thermostats, or both.

T1 and T2 provide power and communications to the thermostat on the end of the wiring. No wonder they're confused... On top of that, you should NEVER parallel power supplies in the way you've done, because unless they're identically matched and designed explicitly for the job, one of them (the one with the highest voltage) will pick up the entire load.

I usually curse the "why didn't you get a professional in to do this" attitude of this place, but "WHY didn't you get a professional in to do this?"

sparkymark75 · 1 Aug 2017

According to Nest, the T1 and T2 connectors are only used for 5v DC to the Nest thermostats as they communicate wirelessly with the Heat Link. You can run a Nest Thermostat using a supplied USB cable without using T1 and T2 at all. I can test it via the button on the Heat Link, taking the Nests themselves out of the equation.

I've updated my drawing as some of the wiring looks like its a shared wire but it's not.

nitro23456 · 1 Aug 2017

But if you use T1 and 2 the communication is wired (and more reliable).

You have been given the correct advice above.

sparkymark75 · 1 Aug 2017

nitro23456 said:
But if you use T1 and 2 the communication is wired (and more reliable).

You have been given the correct advice above.

Okay, it doesn't mention that in the installation guide and suggests it's for 12v DC only but I'll split out the T1 and T2 cables between the two junction boxes and see how I go.

D_Hailsham · 1 Aug 2017

FurstyFerret said:
T1 and T2 provide power and communications to the thermostat on the end of the wiring.

Are you 100% sure about that? My understanding is that T1 and T2 provide power only; communication between thermostat and heatlink is wireless.

What happens when the thermostat is powered locally, from a socket, using the supplied lead. You don't have a connection between thermostat and heatlink in that situation.

FurstyFerret · 1 Aug 2017

Are you 100% sure about that? My understanding is that T1 and T2 provide power only; communication between thermostat and heatlink is wireless.

If thermostat is connected to T1/T2 it'll communicate over these cables. If USB power it'll use wireless. Don't know what would happen in these circumstances as I don't imagine Nest ever considered the situation...

https://nest.com/uk/support/article...e-Nest-Thermostat-communicate-with-each-other

Also, the Nest backplate normally receives 12V from the Heatlink, not 5V. In this setup, assuming you can't connect each thermostat independently to its heat link, I'd suggest you provide a separate 12V supply to both thermostats and electrically isolate them from the Heatlinks, leaving them to communicate wirelessly.

sparkymark75 · 1 Aug 2017

Okay, so I've split out the T1 and T2 connections as per the advice above. It all seems to be firing up as before but still no heat in the radiators. Maybe I need to leave it longer but I would have thought that after 5 minutes, there would be at least some mild warmth in the radiators?

It's currently 22 in my lounge, I've asked it to heat to 25. I'll leave it for 30 minutes or so and see how it goes. The boiler fires up and I get a flame icon on it along with an icon of a radiator.

EDIT: Updated attached diagram.

sparkymark75 · 1 Aug 2017

FurstyFerret said:
If thermostat is connected to T1/T2 it'll communicate over these cables. If USB power it'll use wireless. Don't know what would happen in these circumstances as I don't imagine Nest ever considered the situation...

https://nest.com/uk/support/article...e-Nest-Thermostat-communicate-with-each-other

Also, the Nest backplate normally receives 12V from the Heatlink, not 5V. In this setup, assuming you can't connect each thermostat independently to its heat link, I'd suggest you provide a separate 12V supply to both thermostats and electrically isolate them from the Heatlinks, leaving them to communicate wirelessly.

Isn't that for the older Nests? They certainly don't make it 100% clear what the story is as further down that same page it says; "Even if the thermostat and Heat Link are connected via cables, they’ll still communicate using Nest Weave so that the Heat Link can receive automatic software updates. So it’s a good idea to make sure that the Nest Thermostat and Heat Link are within range, even if they’re already connected by cables."

sparkymark75 · 1 Aug 2017

So the living room radiator still isn't getting warm. The boiler is still heating away. The zone 1 valve is warm and the pipe coming from it is hot. The zone 2 valve is cold as is the pipe.

muggles · 1 Aug 2017

sparkymark75 said:
Okay, so I've split out the T1 and T2 connections as per the advice above. It all seems to be firing up as before but still no heat in the radiators. Maybe I need to leave it longer but I would have thought that after 5 minutes, there would be at least some mild warmth in the radiators?

It's currently 22 in my lounge, I've asked it to heat to 25. I'll leave it for 30 minutes or so and see how it goes. The boiler fires up and I get a flame icon on it along with an icon of a radiator.

You're still mis-wired - you've got both Heat Link Terminal 3's going to the brown wire for Zone Valve 2. You need to move the Terminal 3 wire from Nest Heat Link 1 to the terminal for the brown on Zone Valve

I can confirm that Nest does very definitely use the wires for communication as well as power

sparkymark75 · 1 Aug 2017

muggles said:
You're still mis-wired - you've got both Heat Link Terminal 3's going to the brown wire for Zone Valve 2. You need to move the Terminal 3 wire from Nest Heat Link 1 to the terminal for the brown on Zone Valve

I can confirm that Nest does very definitely use the wires for communication as well as power

Sorry, that's an issue with the diagram as I had to move both of the Heat Link #3 along in the junction box. I have definitely moved them, I just missed that one in the diagram. I will correct it.

The heating's been on for over 30 minutes now. All the radiators downstairs (zone 1) are cold. However, some of the radiators upstairs have heat in them. So I'm thinking theres a combination of two things going on here.

1. The person that fitted the heating has the zones around the wrong way.
2. Some of the radiators need bled.

Possible?

D_Hailsham · 1 Aug 2017

From the Nest Installation Manual (my emphasis):

The Heat Link and Nest Thermostat communicate wirelessly, even if they are also connected by cables.

As for the actual problem ...

Have you checked that the zone valves open when a call for heat is made? Feel the pipe, on the side away from the boiler, some distance from the valve; it should be hot.

What happens if you turn the TRVs up to maximum?

Do the two rads without a TRV (one in each zone) get hot?

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Nest install seems okay but not convinced it's working!

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