topic Gen 3 E74 code no power to Rh, but Rh measures 27 volts. in Nest Thermostats

Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

bill_in_Savanna — Thu, 14 Jul 2022 17:01:49 GMT

Our house has 2 separate heat pump systems, both with Nest thermostats for years. On Sunday we had heavy thunderstorms, but did not lose power. Later in the evening we noticed that one of the systems was not cooling. Error code E74, no power to Rh wire appeared. I did some rudimentary troubleshooting per the suggestions and also measured 27 volts on the Rh wire behind the thermostat. I goggled solutions and found none, though I have found a couple of posts that are apparently the same or similar issue. So I called a pro for $150. He verified the 27 volts on the Rh wire, and checked the function of both inside and outside HVAC units, and found everything as it should be. We swapped thermostats to no avail ("bad" Nest was OK on the other system and "good" Nest returned error E74 on the failed system). We even swapped bases to no avail. Ultimately he installed a conventional thermostat, and it works.....so what is going on here?

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

R6pilot — Thu, 21 Jul 2022 23:51:37 GMT

I can’t explain why this worked for me. I had two issues and swapping RC for RH worked for a few months and then I swapped it back and havent had an issue since February.

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

Ryan_G — Tue, 26 Jul 2022 08:35:15 GMT

Hi bill_in_Savanna,

Thanks for reaching out here in the Google Nest Community.

I'd like to jump in here and check if you've seen R6pilot's response about swapping the wires from Rh to Rc. You could also try doing a restart or reset your Nest Thermostat to refresh and detects the wires from the base.

Let us know how it goes by replying to this thread.

Best regards,

Ryan

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

MelbaDT — Sat, 30 Jul 2022 04:19:07 GMT

Hey there,

Checking back in — how's your thermostat now? Still need our help?

Best,

Melba

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

MelbaDT — Sun, 31 Jul 2022 04:23:41 GMT

Hi,

We haven't heard from you in a while so we'll be locking this thread if there is no update within the day. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

Best,

Melba

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

bill_in_Savanna — Sun, 31 Jul 2022 09:46:26 GMT

I chatted with Nest help and got nowhere. I swapped bases with my other system again and found that

The base of the bad Nest has failed. It is not just a terminal block but contains active components. It appears as an item in the Nest store, but is no longer available. Because of my frustration with support, lack of parts, and the high cost of replacing the whole Nest relative to other systems that are now available that meet my needs, I decided to try a ecobee.

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

MelbaDT — Thu, 18 Aug 2022 11:28:14 GMT

Hey bill_in_Savanna,

Sorry for the delay and we understand how you feel. Rest assured that we'll also take your experience as feedback — we'll ensure to learn from it to be able to deliver a better one in the future.

We're sad to see you go but if you wish to give us another chance in the future, you know where to find us.

Best,

Melba

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

R6pilot — Thu, 18 Aug 2022 11:45:17 GMT

This happened again to me yesterday. I swapped the red over to the rH port and it worked again. I have absolutely no idea why this keeps happening but the fix has worked every time.

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

Jake — Wed, 24 Aug 2022 21:39:32 GMT

Hey R6pilot,

I am glad to hear you were able to fix the issue by swapping the wire. I wanted to check in with you, and see if you had any other questions from here. Please let me know, as I would be happy to take a closer look and assist.

Best regards,

Jake

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

R6pilot — Wed, 24 Aug 2022 23:21:51 GMT

I hope someone has a reason why this keeps happening. It’s great I’ve been able to swap and fix for a few months at a time but what if that doesn’t work one day when it’s cold out? Thanks

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

Jhonleanmel — Wed, 28 Sep 2022 17:57:56 GMT

Hi everyone,

@Jake, thanks for the help here.

@R6pilot, thanks for getting back to us and sorry for the delay. We're always here for you whenever you need help.

Also, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

Jhonleanmel — Sat, 01 Oct 2022 21:40:56 GMT

Hey there,

Checking back in should you still have some questions here. Let us know by replying to this thread.

Best,
Mel

Re: Gen 3 E74 code no power to Rh, but Rh measures 27 volts.

Jhonleanmel — Sun, 02 Oct 2022 22:12:17 GMT

Hey folks,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

Thanks,
Mel