Nest Thermostat and Heat Link communicating, but boiler not responding - wiring at fault?

[MarkJuanFiesta]

Hello.

I've just replaced our Danfoss TP5000 Si Programmer+Thermostat with the Nest Learning Thermostat (3rd gen), which involved the installation of the Heat Link in place of aforementioned old thermostat/programmer. Alas the boiler is not responding to this setup at all.

A couple of things to note, the thermostat will only be used to power on/off the central heating (via combi boiler) same as the old thermostat that was only connected via 2 wires (see pic/s), which is fine, this is all we need it for. As well as the 2 wires there was an unused Earth & Neutral wire (which was 'blocked off') behind the old thermostat which I've used in wiring the Heat Link as just wiring it with 2 wires didn't provide it with power (I had originally only wired the Heat Link with 2 wires, to terminals 2 & 3 which obviously didn't work).

With that out of the way, I have provided a picture of the wiring setup which works insofar as the Heat Link is powered and responds from communication from the Nest Thermostat but the boiler I fear is not getting information from the Heat Link as it doesn't respond. It doesn't respond either to pressing the button on the Heat Link.

I have put the old thermostat back in place for now and the boiler is working fine but would love to get the Nest up and running instead.

Thanks in advance if anyone can advise where I've gone wrong.

[AlexD]

Thank you for all the information provided @MarkJuanFiesta . I would be happy to try and assist. 

That is how we'd expect to see the wiring on a combi system. Live and Neutral in the N and L terminals, a bridge from L to 2 and the call for heat wire in terminal 3.

To confirm, the Heat Link has a green LED on it, correct? 

We want to do some tests to see how the relays in the Heat Link behave. Go next to the Heat Link and open the Nest app on a mobile device:

1. Select your thermostat to access the heating controls and make sure the screen is black, heating is off.
2. Turn up the temperature until the display goes orange, heating on, and listen for a clicking noise.
3. Turn the temperature back down until the display is black again, heating off, and listen for a clicking noise again.

Let me know what the results are.

[MarkJuanFiesta]

Hello Alex. I'm pleased you were able to confirm the wiring is as expected. At the moment my old thermostat/programmer is connected to the boiler but I am able to confirm that when the Nest thermostat and Heat Link were installed, the Heat Link green LED was lit. I also did the steps 1. 2. & 3. as you suggested and did notice a clicking sound. I can install the Nest again later this week to try this again but am happy if you could suggest any other reason the boiler did not respond to these steps last time?

Many thanks, Mark.

[AlexD]

You can only have the Heat Link connected to live and neutral and that would be enough to have it active and tested. The diagram on the old thermostat seems to be similar to the 1,2,3 relays located on the Heat Link. You have live power going in the middle and the relay is usually closed on the left terminal when there is no need for heat, empty with no wire, and bridges over from the middle to the right when heat is requested, connecting to the black cable there. 

Heat Link does the same thing. Power is delivered in terminal 2 that is usually bridged to terminal 1, which is empty and when heating is requested it should move over and bridge 2 and 3, where the call for heat wire would be. 

I see the cable for the bridge there may be a stranded multi core wire. Try if possible to get a single core wire for the bridge, as that would be best. 

However, if you mention it clicks both when turning the heating on and off, that would usually indicate that it's working as expected.

Do you happen to have a multimeter at the location that you are also comfortable in using to perform a continuity test? 

If you are able to do so and are comfortable to do so I can send the steps over the email associated with your account here or if you have an installer that you wish to perform it for you, you can provide the steps to them. This way we can say for certain if something unexpected is going on in the Heat Link as by just the clicking tests, it seems to be working as expected.

[MarkJuanFiesta]

Alex, thank you for your suggestions. I will get hold of some single-core wire for the bridge and try that. I do not have a multimeter but I can buy one if needed and if you send me the email I will take those steps also after I have changed the bridge wire as suggested. Many thanks, Mark.

[TudorL]

No worries at all, please let me know if me or my colleagues can do anything else for you. 

[Vladut]

Hi there, just checking in with you. Do you still need help?

[MarkJuanFiesta]

Hello Vladut. I managed to get the Nest Thermostat working fine now thanks. I suspect a loose live bridging wire was the culprit. Kind regards, Mark.

[TudorL]

Got it. Is there anything else me or my colleagues can do to help you out? 

[Vladut]

Hi there, just checking in with you. Do you still need help?