topic Re: Nest 3rd Gen with heatlink, T1 & T2 terminals in Nest Thermostats

Nest 3rd Gen with heatlink, T1 & T2 terminals

a3_mike — Wed, 09 Nov 2022 19:30:05 GMT

Dear Community,

I need some clarification on the use of T1 & T2 terminals on the thermostat and heatlink. My question is whether they are used for 12VDC power only, or they are additionally used for comms. The reason I am asking is because there appears to be a confusion on this matter over the internet and I would like to install the heatlink in the boiler room, out of Thread range.

Any expert advice would be greatly appreciated.

Thanks in advance.

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

CoolingWizard — Wed, 09 Nov 2022 20:06:17 GMT

You guys Europe have the added problem of those high voltage heating system. You can use T1 and T2 if there is a cable already there, it is not required to be used, but it can be used. The Nest Thermostat used with a Heat Link uses wireless technology to communicate with each other.

Ken, The AC Cooling Wizard (In America)

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

a3_mike — Sat, 12 Nov 2022 10:04:11 GMT

Thank you very much for the prompt answer. I am already familiar with the wireless functionality as I already have 1 Nest 3rd gen in my home working like that ( heatlink installed at the location of the old thermostat, and thermostat located on a shelf, powered by USB on a nest stand).

As I am renovating the house, I am curious whether I could move the heatlink in the boiler room (out of wireless range) and use the existing pair of cables for power AND comms in order to install the nest on the wall.

I would really like to go for the "clean" installation where only the nest is visible on the wall, similar to a US installation.

It is not clear to me whether the T1-T2 terminals support communications concurrently with 12VDC power delivery.

Thanks in advance

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

CoolingWizard — Sat, 12 Nov 2022 14:18:29 GMT

Mike, the T1/T2 are power only, there is no communications over it. The Heatlink and its paired nest thermostat always use a special variation mode of Bluetooth to communicate.

Ken, The AC Cooling Wizard

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

a3_mike — Sun, 13 Nov 2022 11:31:13 GMT

Thanks a lot for the info and your time!

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

Max71 — Tue, 20 Dec 2022 17:09:43 GMT

Hi Ken,

I'm about to install a nest thermostat here in the UK. My question is whether I can use T1/T2 on the heatlink as a 12V source to power a 230V solid state relay to switch a 3kW immersion hot water heater via the hot water relay - the current drain will be minimal ... many thanks in advance .... Max

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

CoolingWizard — Tue, 20 Dec 2022 19:22:13 GMT

MAX, I am in the USA and do not use nor have I installed a Heatlink sense those are for UK.

Ken

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

Max71 — Tue, 20 Dec 2022 19:26:42 GMT

Hi Ken,

Thanks for the reply I thought you would know because you answered about the Heatlink T1/T2 above in this thread - is there anyone else here who can help me ?

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

CoolingWizard — Tue, 20 Dec 2022 19:50:08 GMT

When I get the model information I can look up the mfg manuals and figure most things out. However here the problem. The T1/T2 can be used if it can be verified that it is low voltage and not high voltage.

Ken

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

Max71 — Tue, 20 Dec 2022 20:03:50 GMT

thanks Ken - definitely 12V

Max

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

a3_mike — Tue, 20 Dec 2022 23:03:16 GMT

T1-T2 are 12VDC. Verified with a multimeter.

However, following my previous exchange with Ken (whom I would like to thank again for his time and interest), and since the thermostat was giving me the option to set it up without a wireless connection to the heatlink, I found out that they are also used for comms. There is full functionality, albeit a couple of seconds slower than with wireless enabled, and the thermostat indicates that its connection to the heatlink is wired only. Additionally, no pairing is required in this case. For some reason, Google - Nest is a bit vague on the matter.

Therefore, I do not know what the effects of sticking a load at the other end of T1-T2 would be for the circuitry of the heatlink.

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

Max71 — Wed, 21 Dec 2022 10:14:01 GMT

Hi Mike,

Very many thanks for the reply. Interesting ... So that proves that T1/T2 are used for comms when wireless not enabled. It may be really too dodgy to draw any current from these terminals for my power relay. My other solution of course is to get a relay with 230V input switched using the hot water control relay of the the Heatlink.

Thanks again, Max

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

a3_mike — Wed, 21 Dec 2022 10:39:42 GMT

Using a 230VAC relay is the reasonable choice here. After all, this is what the Hot Water terminal on the heatlink is for.

Re: Nest 3rd Gen with heatlink, T1 & T2 terminals

Max71 — Wed, 21 Dec 2022 11:16:00 GMT

Thanks for the reply - yes I’m sure you’re right ! It’s just that I have 12V input power relay to hand … all the best Max