Mounting plates buzzing for inactive zones when another zone is active after installing Nest Power A

[mjdavidge]

We've had three 3rd gen Nest thermostats running for a few years now where the only issue is the battery will sometimes drain and cause connectivity issues, as the HVAC tech installed them with resistors bridging the R and C connections in the valce control unit (due to it being an older house with only R/W to the stats).

Another tech recently pointed out the Nest Power Adapters that are intended to deal with this issue of a missing common, so I purchased and installed 3 of them.

Was very careful to take before/after pictures and ensure everything matches with the wiring connections, and the stats seem to run fine, but I've noticed that when at least one zone is running, any zones that are NOT running will have a constant low buzzing sound at the wall plates. This sound will stop if:

1. ALL units are off

2. The unit is one of the ones actively calling for heat

3. I manually push down on other connectors on the wall plate, as though I were going to insert another wire (buzzing starts up again when released)

I've seen some other posts on here that are now locked, but none of them seemed to have a satisfactory resolution on how to solve it, so I'm opening a new thread in the hopes of getting one.

Thanks all!

[catheryn]

Hi @mjdavidge, 

Thank you for bringing this issue to our attention and posting it in the community. I apologize for the inconvenience you're experiencing with your thermostats and Nest connector.

I understand the main issue seems to be the constant buzzing sound coming from the mounting plates of inactive zones.

Before attempting any troubleshooting steps, please share a photo of the control board and any labels it may have. 

Thanks in advance, 

Catheryn. 

[mjdavidge]

Hi Catheryn - that's 99% correct. The issue is the buzzing sound coming from wall plates of inactive zones, however its only present when at least one other zone is active. If all zones are inactive, it stops.

I'll attach the before and after pictures from my Taco box (apologies in advance that it's a bit spaghetti-fied). I did not use the included sticker labels because they would have stripped off going through the access holes, but I did triple check that the wires were all matched up correctly (i.e. White R/W/C from adapters go to R/W/C on Taco, and Gray R/W go to the wires that had previously been in each R/W Taco slot).

 

[catheryn]

Hi @mjdavidge, 

Thanks for your reply and the additional information. 

Once we've inspected the current wiring, we can determine the cause of the buzzing noise. The power connectors may be connected incorrectly. We recommend reverting to the original wiring configuration and contacting a Nest Pro technician. They can provide expert guidance and ensure the wires are connected securely and correctly.

Use this link to check useful information about contacting a technician:

OnTech - Smart Services 

Professional installation services

Let me know how this goes. 

Thanks, 

Catheryn. 

[mjdavidge]

Hi Catheryn - respectfully, I feel like the wiring is correct, as it was a pretty straightforward install... the correct leads from the thermostat are paired with the gray wires from the adapter, and do not come loose from the wago connectors, while the white wires from the adapter are securely screwed into the Taco box. Nothing is loose, disconnected, or touching other wires, so this feels like something else.

In my case, the thermostats all work correctly (buzzing aside), and the big thing that stands out if I use a multimeter on the R(C) / W(1) connections at the mounting plate is that the voltage drops as other zones activate... i.e. I'll register a constant 25.3 if no zones are running... then if I flip a zone on, that'll drop to ~25.1 and wobble slightly... ...turning on a second zone causes a drop to ~24.5... then once both zones are off, it'll jump back to 25.3.

What's not clear to me is whether or not that is normal behavior (due to the power stealing behavior when zones are on), and whether this is a case where that slight dip in power is causing that increased buzzing at the plate. 

Are there any spec sheets for how much extra voltage the Adapters draw, on top of what the Nest thermostats themselves draw? Based on some older posts, I'm wondering if it's a case where this board was fine with 3 valves & 3 Nest stats (with resistors bridging the W/C connections), but the Adapters are potentially pushing the power draw over.

[catheryn]

Hello @mjdavidge,

Thanks again for your response. 

Indeed, the behavior you're experiencing is unusual. That's the reason we recommend contacting our specialists for a diagnosis. 

They can determine if the issue is related to the wiring or the thermostats.

If the problem is with the wiring, our experts can assist you in resolving it and ensuring your devices function correctly. If the issue lies with the thermostat, we can review the warranty dates and guide you through the replacement process or other appropriate steps. 

Let us know if you have more questions about this process. We are here to assist. 

Regards, 

Catheryn. 

[mjdavidge]

I can't imagine those specialists are a free service, which is why I was hoping to get support via this avenue in case there was a known issue with that use-case of 3 stats with adapters on a standard board.

I'm sure my Nests are well out of warranty at this point, but the 3 adapters are still within the return window for another week or so - if I can't figure this out by then, I'll likely have to revert back to the original wiring with the bridged resistor common and just return them.

[catheryn]

Hi @mjdavidge, 

Thanks for your response. 

Please let us know if you need further assistance or help to resolve any issues with your Google Nest devices. 

We are here, ready to assist. 

Warm regards, 

Catheryn. 

[mjdavidge]

Thanks Catheryn - given we weren't able to resolve it, I reverted the wiring to the previous "resistor as a common bridge" configuration, at which point the buzzing stopped, and have initiated a return of the three adapters.