topic Re: H72 - Heat Link dead in Nest Thermostats

H72 - Heat Link dead

Nickbr — Sat, 02 Sep 2023 10:00:53 GMT

Hello,

Our Nest thermostat stopped working a while back and today I found some time to debug the issue.

As the thermostat was empty I charged it (off the wall mount) by usb, after charging and placing it back on the wall it gave a H72 error/not having power.

I checked and measured all cables and found that the heat link is defective as it does have 230Vac but no lights are coming on, even when pressing the button for 5,10,15,30 and 60 seconds.. Also I could not measure any output voltage on the thermostat terminals. After some searching i found big clives YT video and tried the powerbank on the usb, this does active the device and makes the leds turn on (running the µC). So I guess i have the issue that is also described in that video. Is this a known fault and what should I do (before I start replacing that smt diode)?

Regards,

Nick

Re: H72 - Heat Link dead

Frustratedddd — Sat, 02 Sep 2023 22:16:42 GMT

Why repair when you can ask for a replacement?

Once you touch the Heat Link your warranty is void.

I assume you are UK, which means you have consumer rights for at least 5 years for an item like the thermostat. Spend time looking into those, you will be suprised.

Plugging a USB into that port doesn't really confirm that problem, it's a guide that's around the net for ebay sellers to get your repair to them. Having said that, I would probably say it's the issue like 99% of Heat Links.

Re: H72 - Heat Link dead

UanaC — Sun, 03 Sep 2023 10:16:41 GMT

Hello there @Nickbr I'm really sorry to hear that you've encountered issues with your Heat Link and I'll do my best to help you out. Can you please answer these questions:

1. How long has your thermostat been installed for?
2. What is showing on the Nest thermostat display?
3. Have you had any power cuts recently?
4. Have you had any work done on your electrical or heating systems recently?
5. How many zones are present in the setup?

Re: H72 - Heat Link dead

Nickbr — Sun, 03 Sep 2023 11:15:42 GMT

Because repairing would be a 5 min job for me. But I posted this message indeed to check what my warranty would be. Especially because this seems to be a known problem.

The usb powering does verify the µC to be working, and for as I have seen/read it almost definitely indicates the 12V bus power issue.

Re: H72 - Heat Link dead

Nickbr — Sun, 03 Sep 2023 11:13:44 GMT

2-2,5 years
Well, it is empty now, but when I charge it like mentioned in my first post it gives the heatlink error: "power to this thermostat is off. Learn more at nest.com/H72"
No power cuts
No
1 Zone

Re: H72 - Heat Link dead

Frustratedddd — Sun, 03 Sep 2023 11:53:28 GMT

............in that case over to UanaC

Good luck!

Re: H72 - Heat Link dead

UanaC — Sun, 03 Sep 2023 12:05:59 GMT

Thanks so much for everything @Frustratedddd! Got it. Can you please confirm if you've tried these troubleshooting steps:

1. Check if all the breaker switches are set to on.

2. Turn them off and back on.

3. Try to turn on manual mode.

Also, may I contact you over the email address you're using here?

Re: H72 - Heat Link dead

Nickbr — Mon, 04 Sep 2023 17:23:11 GMT

1. They are on.

2. Already did that before my first post but tried again just to be sure, nothing changed. Also I measured the 230Vac on the input again and it is still there. To be sure i disconnected all other wires except the 230Vac just to see if the light would go on and there is no strange short circuit. but this did nothing.

3. This is not possible as it is completely unresponsive, I might be able to try this with the USB power but i can't see the point of that?

Yes, no problem. you can use my email.

Re: H72 - Heat Link dead

TudorL — Tue, 05 Sep 2023 10:10:06 GMT

Thanks for all the info you've provided. Would it be okay if I send you an email to the address associated to your Community account?

Re: H72 - Heat Link dead

Nickbr — Tue, 05 Sep 2023 10:11:23 GMT

Yes i am ok with that

Re: H72 - Heat Link dead

TudorL — Tue, 05 Sep 2023 10:25:15 GMT

Great, I'll send it right away.

Re: H72 - Heat Link dead

UanaC — Thu, 07 Sep 2023 15:48:03 GMT

Hello there @Nickbr ! Just checking in. Did you receive my colleagues email?

Re: H72 - Heat Link dead

MrMarmac — Fri, 08 Sep 2023 07:55:00 GMT

Hi @UanaC not to piggy back on here, but I am experiencing the same issue as above. I'll answer the same questions if that's ok?

1. How long has your thermostat been installed for?

26 Nov 2020

2. What is showing on the Nest thermostat display?

H72 Heat Link The Power to this thermostat is off. Learn more at nest.com/h72. The heatlink has no lights on when connected to mains, but power has been tested to the unit. Plugging in a USB plug brings up a yellow status light.

3. Have you had any power cuts recently?

None

4. Have you had any work done on your electrical or heating systems recently?

Any help muchly appreciated!

Martin

5. How many zones are present in the setup?

Only 1 with one thermostat connected by wired backing plate on the floor below.

Re: H72 - Heat Link dead

MrMarmac — Fri, 08 Sep 2023 07:57:48 GMT

1. Check if all the breaker switches are set to on.

They indeed are.

2. Turn them off and back on.

I have cycled these now

3. Try to turn on manual mode.

The unit doesn't respond on mains, but does respond on usb. The 2 lower lights go green, but doesn't seem to activate the heating or hot water. Pushing the button again disables the 2 green lights.

Re: H72 - Heat Link dead

MrMarmac — Fri, 08 Sep 2023 10:13:06 GMT

Good on you @Frustratedddd , can see you've been advising people on these for a few years now. Wouldn't have known where to start until a quick online search brought me here. Thanks!

Re: H72 - Heat Link dead

AlexD — Fri, 08 Sep 2023 14:05:39 GMT

Hi @MrMarmac , thanks for reaching out to us here. I am sorry to hear you are facing the same behaviour with your unit and I would be happy to try and assist.

Thank you for all the information provided and troubleshooting done.

Would it be ok if I reached out to you over the email associated with your account here so we can look further into this?

Re: H72 - Heat Link dead

MrMarmac — Fri, 08 Sep 2023 14:16:10 GMT

It certainly would 🙂 the one on this account is fine thanks!

Re: H72 - Heat Link dead

AlexD — Fri, 08 Sep 2023 14:18:45 GMT

Awesome, just sent the email your way with the form. Once you fill it out let me know here so me or one of my colleagues can look for it.

Re: H72 - Heat Link dead

MrMarmac — Fri, 08 Sep 2023 14:53:15 GMT

Filled out and submitted now thanks Alex!

Happy Friday,

Martin

Re: H72 - Heat Link dead

AlexD — Fri, 08 Sep 2023 14:56:13 GMT

Thanks for letting me know. I'll be in touch over email with further details.