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Nest Thermostat Error N72

FrankieJ
Community Member
Error N72: "Power wire Rh detected. No connection to equipment." 24VAC confirmed.
I recently installed a Gen 3 Nest Thermostat. We have completely separate heat and Air Conditioning systems. 
 
From our standard, ducted air conditioning system we have four wires:
  • Y
  • G
  • Rc
  • C
 
From our very basic, boiler-and-radiator based oil heat system we have 2 wires:
  • W
  • Rh
 
This has worked for years with a battery-powered, programmable thermostat. In the winter, we cut the circuit breaker from the air conditioning system, so all we have is heat, using W and Rh.
 
Installed the G3 nest yesterday and it reports: "Power wire Rh detected. No connection to equipment. Learn more at nest.com/n72".
 
A few things to note:
  • The Tech Info diagram on the unit itself shows "power" greyed-out on Rh. 
  • Testing with a digital multimeter between Rh and W1 shows over 24VAC consistent.
 
 
Thoughts? Thanks for any help you can provide!
178 REPLIES 178

Jpbone120
Community Member

Just installed the T9, like the others. No more heat issues or error messages 👍🏻

carol5516
Community Member

I'm having this same problem - with the same results from my hour-long chat with Monika. As a senior with absolutely no tech skills or knowledge, I assumed I was being stupid or doing something wrong. I am so sorry that so many people are experiencing this problem - I don't wish it on anyone (especially living in upstate NY on the first day of winter!!). The HVAC people who installed my new furnace system in May (and installed the Nest because I thought it was a good idea!) are coming out in a few days to check things out. I'm seriously thinking of asking them to install the thermostat that they originally wanted to use (programmable, but not 'smart') and get rid of this nasty Nest. For now - I'm just grateful for space heaters!! Take care everyone, stay safe and warm!

 

Chobes
Community Member

Sorry to hear Nest has claimed a new victim. Did you test the heat when it was installed or this is the first time testing the heat?

carol5516
Community Member

The Nest was installed in April when I had a new furnace/hot water system installed. I thought the Nest would be a good idea! It was tested with both heat and A/C and it was working fine until a few days ago. Now I seem to be getting every error message tossed at me randomly - no internet detected - then later it's magically connected to the internet - then it's gone again - no power - then it just starts heating - then it stops. There's no logic or power to the error messages (or when the things works or doesn't). Most common message is 'E72 - Power wire Rh detected. No connection to equipment.' The HVAC folks are coming tomorrow (they're really busy so they couldn't get here any sooner). Right now all I want is for them to remove the Nest and install a nice simple programmable thermostat! I'm too old to be this cold for this long!! (sorry for the rant. I'm just so frustrated!!).

Chobes
Community Member

Sounds like the same issue! If you have the time, please share what the HVAC company said and did. If you want a manual method of running the heat you could pull off the Nest from the base, unplug the Rh and W1 wires from the base and touch the copper ends together using a chip clip or similar. Don’t touch the exposed ends with your hands. The ends touching will send the signal to turn on the heater. When it’s warm enough and you want to turn the heat off, just remove the chip clip so the wire ends are not touching each other 

Chobes
Community Member

Hello, what did the HVAC company have to say?

carol5516
Community Member

Good morning! Sorry I didn't get back to you sooner - I was basking in the warmth of my new, non-smart, programmable thermostat! The HVAC guys were wonderful - but they were as confused (and angry) as I was about the whole situation. While they were here, the Nest proceeded to go through its never-ending list of error messages and turning on & off for no reason. So, at least I was glad that they were experiencing the same craziness that I was. We went through the usual routine - fiddled with the unit to try and 'fix' the problems listed in the error messages - turned the router off and on to try and reboot everything - checked the wiring (and assured me that the wires were all correctly attached in the right places). They checked the furnace controls in the basement - they checked the air conditioner controls in the attic. You name it - they checked it. They were, by the way, VERY upset that Lady Monika of the Chat had suggested that I work with the wiring (after I had told her that I was a 72-year old woman living alone with absolutely no experience in electrical stuff or 'smart' technology). Finally I asked if they could just remove the Nest and install the non-smart programmable thermostat that should have been installed in the first place. They took care of that - checked everything again - wished me a Merry Christmas (it was Dec. 23rd) - and left still shaking their heads over the craziness I had endured.

So now I have a working thermostat - and (I guess) a new paperweight called 'Nest.' I want to thank everyone in this group that listened to me whine and put up with my complete lack of understanding about this whole issue. You folks performed a great service in alerting me to the fact that I was not the only person on the planet who was experiencing these problems - and I am very grateful. I wish you all great success in solving your problems with this creature named 'Nest' - and my sincere wishes for a happy, healthy, safe, and WARM New Year!!

Chobes
Community Member

Thank you. Glad it is resolved.

Wish the same for you!

Norman
Community Member

Here with the same issue. System and Nest Gen 3 have been working for the last 2 years with no issues, then about a month ago I noticed the heat not coming on in this zone. I have 3 other Nests running in the house with no issues (2 e and another 3rd gen). I had a new unit installed in a different part of the house and had my HVAC tech check the one that wasn't working. He tested everything and said it was the thermostat. I checked and sure enough N72 error. I tried to reset it to see if that would resolve the issue, but now it won't connect to either the Nest or Google home apps as well.

I went on support thru chat and like others here did the "trouble shooting" to finally have them say it's the base and that I need to replace it. Besides someone above saying they replaced theirs with no luck, they are also not in stock: https://store.google.com/us/product/nest_learning_thermostat_3rd_gen_base?hl=en-US

On a side note - while doing the troubleshoot, I did notice that the RH came back on once the AC was completely disconnected. Obviously this is not a fix, but it can at least get it to control the heat until there's some resolution to this issue.

I'm hoping someone can say they replaced their base and the issue was resolved before I spend more money on this thing. I am also considering switching to a Honeywell thermostat if this is how Google plans on dealing with what seams like a new problem. 

Nickvaf
Community Member

Same issue as everyone here. System confirmed working fine at boiler and all other thermostats and gen2 nest work, but gen3 gives the N72 error. Software but that caused this? Was working fine last 2 years. 

gp1200x
Community Member

Their auto updating caused it since you have Internet capability and these FF**F things can auto-update.

Google should be sued since it has been going on too long. Same crap with Philips and their CPAP machines. Both companies need to be put out of business.

gp1200x
Community Member

I bought 4 Nest thermostats----SHOULD HAVE BOUGHT THE ECOBEE like I did for my family members. ECOBEE works great. These NEST truly are junk. I spent days rewiring and trying to figure out WTF was going on. Then I went to the Internet and starting reading. If you have two separate systems with different transformers on different phases your are SCREWED with these units. I had no issues with any other makes excepts for the Google NESTs. If you just bought them take them back!  They  are no good in the Northeast if you have 2 separate systems. All four of my NESTs fail with the N72 error. Fortunately they work because the units are only a year old. Older units with old internals appear to be failing with the N72 and disabling the heating side. Regardless....the issue is a software failure by some idiots at Google that appear only have a fifth grade education with no electrical skills in the real world. The state attorney generals should file a suit against Google to recall the units before older seniors end up freezing to death. Pushing out bad software to working units (without notification in the least!!) should be grounds for a lawsuit!  It happened to MS and should happen to Google. 

Chobes
Community Member

where do I sign? I would at least want my $310 back ($250 for Nest + $60 for the new base they said I needed)…

saiyanavatar
Community Member

I'm having the same issue, spent an hour with chat support yesterday who hung up on me after referring me to a paid $99 an hour service and spoke with customer service for about 2 hours and 10 minutes after a 30 minute wait.

They said they're replacing both the base and the front unit, but I'm not optimistic.  They said they wouldn't couldn't provide a refund.

You certainly have my sympathy, and thank you for posting here. Please keep us posted if you can (if you get the replacements, do they work? If so, software/hardware version numbers?)

Myself, I have been working on many smarthome projects recently and haven't made the time to call in, and I'm very thankful to the people who have. I'm using my old thermostat which works perfectly but really wish I had the smart thermostat I paid so much for, same as everyone else here.

gp1200x
Community Member

Conclusions for me.
First off here is my setup...Heating and Cooling. Two complete separate systems that do no interconnect....just like 50%+ of the homes in the Northeast. Baseboard oil with radiators when built in 85 and central air added in 91. Used 3M Wifi with Radiostat for years with NO issues ever except transformer burnouts. Four heating zones and two cooling zones - 2 floors.
Bought NEST Learning thinking they would be great - WRONG choice after installing ECOBEEs in family members house which they love and work great with no install issues.
In my type of setup the N72 error issue appears and I have NEVER found a way to resolve it. The software update pushed out appears to have caused the issue. I doubt you can stop updates unless you want to completely lose your remote access option, but if that's okay then put rules in your firewall. Both of my systems work however my NEST are probably only slightly more than 2 years old. People that bought earlier NESTs probably have different firmware and hardware in their NESTS and I suspect that is why there systems are now failing with the N72 error. There is probably no way to fix these older units without reinstalling older software which you can't do on your own. You are probably screwed unless you buy new or other manufacturer units - I personally would never buy another Google product. So older units that stop functioning after getting the new N72 error after the update - you may be screwed and broken for life even with another software update....hard to tell if they will resolve your issues in a timely manner!
In my case my units are "somewhat new" so they still work even thought my RH is greyed out and I get the N72 error. I will have to just live with the N72 and wait to see if a software update ever fixes it - I highly doubt it. That also brings us up to those who have the same setup and no errors... They may have later hardware and firmware so they do not display the N72 error. Someone mentioned that using a single transformer for heating and cooling may not produce the error. I doubt it but in any case this is not an option for millions of people in larger homes with dual systems.
At one point someone mentioned that the phasing of the transformers may be the issue. My oil transformers are all 120/40 but my heating was 240/40 so there is a potential voltage difference between the transformers and I could measure it. I was going to rewire my AC transformer to see what happens but that is a lot of work and risky. Instead I added another test transformer on the same phase as all my heating transformers. I wired it up to dummy the NEST to thinking I had heating and cooling and guess what -- SAME ISSUE. IT IS NOT A TRANSFORMER phasing issue. Their software SIMPLY DOES NOT WORK WITH TWO SEPARATE HEATING AND COOLING systems. End of story - GOOGLE F***KED it up!! POOR programmers that do not know what they are doing or how all the systems HVAC work. This is not fixable by the homeowners.
Next issue. People are turning their cooling systems off in the winter....why???? There is no reason for this. LEAVE IT ON. It is barely using any power except for the transformer power. I have no idea why anyone would be shutting down their AC system power - makes no sense to me and you SHOULDN'T BE DOING THAT!!! In the thermostats you can have two systems setup and SIMPLY tell the unit to use HEAT ONLY! Your AC will never come on. You still have the option to use your fan blower if you just want to move air too.
CONCLUSION - STAY AWAY FROM ANY GOOGLE THERMOSTAT MODEL - You never know when they will push out an update to break it...and it could be in winter when you are NOT HOME and your pipes freeze!!!!

GOOGLE - YOU MAKE CRAPPY THERMOSTATS, STOP MAKING THEM!

Chobes
Community Member

Mine wouldn’t work even after turning the AC off. My common wire comes from the AC. I tried adding in a relay from my boiler to create C wire on that system but it still gave me errors and wouldn’t work. 
i wish I could get my $300+ back…

I had to turn it off and unplug the W wire, as if I don't it starts with the heating

Followup: I received my refurbished replacement and had a heating professional come to the house.  There was a separate issue with the boiler that was fixed, but the wiring was confirmed to be working properly.  Unfortunately, the rH wire was still grayed out and the thermostat wouldn't work.  We tried using the faceplate from the other zone (which is still working fine and only connected to heat) but that one had the same greyed out wire.  We installed the new baseplate and things got even worse - everything was greyed out except for the W1.  The new faceplate had the same issues with both the old and the new baseplate.  We tried mixing and matching and even tried installing just the heating wires to one but nothing would work.

After about an hour worth of work, the heating professional installed an old school thermostat for now.  I followed back up with Nest support and they're sending another replacement, we'll see how that goes.  Wish me luck...

Following up again.  Google sent me a third replacement, this time a new unit.  I installed it to spec, discussed it with two separate technicians and had a variety of new errors.  Different errors too!

Luckily, the second technician was able to get me talked down off a ledge in that the unit would not work at all with the AC unit installed.  I was able to install the HEAT ONLY because, you know north east winters.  Cold.  Heat is good, better than no heat, yeah?  Even if the unit wasn't working perfectly, it was working...some of the time.  At least the heat was coming up even if it wasn't always smart...not like I paid for it to be a smart thermostat BUT it did work so there is that...

Ultimately,  due to no C wire being connected, it keeps losing power and wifi connectivity.  I didn't mind so much but now that it's almost time for summer, guess what I will need?  Air conditioning!  And guess what I still don't have working or operational?  Air conditioning.  Spoke to a variety of technicians, had my call dropped by the first who decided not to call me back despite me giving my callback number and him having my prior case numbers, second technician offered for me to pay for a technician to come to my house despite me paying someone to install and a heating professional to try and get it working.

Now on hold with technician #unknown.  I have spent so.  Many.  Hours. Of.  My. Life.  On this.

Like Cher, I wish I could turn back time and not buy these infernal google machines, get my money back from my electrician, get my money back from my plumber.

Or, get google to fix this issue.  One or the other.

I think we all learned it won’t get fixed so everyone has moved to a different thermostat…

Just a followup…turns out my AC unit had a blown fuse.  As a result, once the fuse was fixed, the thermostats have been working fine since.  While it turned out not exactly to be a Nest issue, it was a huge pain to get it figured out.  What I don’t understand is why it needs the AC hooked up for heat to work.  Whaddya gunna do?

ntmagic1
Community Member

This thread has been super helpful. Exact same problem here. I have a common so it still runs fine, but same scenario as other described. Common is from AC handler, Rh greyed out. Bought the unit in October and been a problem since then. Now my issue is that I need to disconnect the AC air handler to get to some work in the attic, which will then kill me heat. So I’m not sure what to do, I guess by another thermostat. It is resale a shame that Google hasn’t fixed this, even after others on this thread seem to have pinpointed the issue!

Mikeya
Community Member

Out of curiosity, has anyone escalated to BBB? I would love to join in or start a fresh complainant there!

SofianeMTL
Community Member

I don't know what BB is and I have not reveived any help from NEST. It is really bad I had the electriciean twice, on top of the nest price I had to pay 600$ more in electrician time

gp1200x
Community Member


Before I start here are some precautions for those doing there own work!
1. Do not overload transformers. If rewiring your heating system remember this...a zone valve for heating uses about 8VA, putting just 5 zone valves on one 40VA transformer is too much. Best to use a larger 75VA unit or better yet add two 75VA and split the zone valves between them. Only buy 75VA transformer with BUILT IN Circuit Breakers if you end up needing to replace any transformer! 40VA is TOO small nowadays. If you overload a transformer you can either burn it up or it will not have enough current if all your zone valves call for power at once which will happen in the dead of winter - result is no heat and possible frozen pipes. Remember too that your Wifi is now drawing .2 amps of power from your AC transformer all the time and putting a small new load on that.
2. DO NOT leave the secondary side (24 VAC)of the transformer open (unconnected) with no load while the primary side still has power. I have a bunch of Honeywell transformers that I did this to and they either fired the secondary wire inside or blow an internal fuse. Not repairable. Not sure how long it takes but I know it is less that 3 hours. I can reproduce this at will...trust me, I did it 3 times.
3. DO NOT SHORT the two connections on the 24 VAC side. I think it takes less than a minute, probably only a few seconds before you will fry the secondary wiring and need a new transformer.....the 75VA one with the built in circuit breaker...mine are now made by RIB.
4. If rewiring ONLY install 18/7 wire runs to the thermostats. Anything else is a waste of your time even if the TSTAT is for heating! Pay the extra for the additional wirings and just coil the spares at each end. If a few years you may need more wires again!
5. Keep a spare transformer on hand for the heating and cooling. I use the 120V 75VA units for the heating and my AC needs 208/240 VAC units.

On to the NEST crap.
BBB - Better Business Bureau I wouldn't count on them if your life depended on it. Google probably has them in their pocket.
Phasing - this is not causing the issue of the N79...I test it and it made no difference. Error and screen displays are all a software programming error made by Google and complicated by having different firmware in their base wall units and thermostats that reacted differently - some worked still with the errors displayed and some failed to work with the errors displayed.
My NEST are 2 to 3 years old I bought 4 NEST Learning thermostats and finally got around to install them. I DO NOT LIKE the learning feature and disabled it...too much of a nuisance. I do not follow the same routine everyday...maybe for some it is okay but not me. These are no better than the old 3M Wifi units I installed 10 years ago with the RadioStat app that was free.

I rewired my entire house for the heating and cooling...too many old 2 and 4 wire lines so I redid them all. 7 wire to thermostats and 5 wires from AC units to my basement. I have a common area where all my wires end up near the furnace and that is where all my line connections are made. I have at least one spare wire an every run to everything. I spent about a week to two doing all this a few hours a day.
ERRORS...as soon as my NESTs were installed they updated and I saw the errors starting to show up. 2 of my Nests are connected to separate heating and cooling systems and the other 2 Nests are for heating only.
The 2 connected to the heating and cooling have 6 wires to the thermostat (2 from cooling, 2 from heating). I got the dreaded N72 error with the greyed out RH even though it shows as being connected. All voltages are correct and my unit is pulling 200 milliamps. MY UNITS STILLWORKED CORRECTLY.
UPDATED - TODAY MY RH IS NOT LONGER GREYED OUT???? I ALSO NO LONGER SEE the N errors. MAYBE THEY PUSHED OUT AN UPDATE.
My other two Nests for heating only have 2 wires RH, W for the heat and I added another transformer and wired it up to provide separate C power with wires to the RC and C. The other day I was seeing N72 errors and the RH was greyed out but NESTS still worked and drew 200 mamps. Today the RH is still greyed out, they still work but I no longer have the N72 error pop up when in the Equipment function. THEY WORK so that is it for me unless they push out another update and screw them all up. They SHOULD NOT BE ALLOWED TO DO THIS WITHOUT OUR PERMISSION SINCE THEY COULD KILL SOMEONE!

Chobes
Community Member

What software version is showing in your Nest now?

 

Can someone else please check if their Nest no longer gives them errrors?

still does for me

gp1200x
Community Member

My Technical screen shows 6.2-22 dated between Jan 3 and Jan 21 on all 4 of them --       so that does not look like it updated.

My BASE shows 1.538/3.1  model backplate 5.4 on all of them.

The two that are attached to both an AC and heating system also show display model 3.4 These both are now showing all 6 lines with none greyed out and I have not seen any N errors on any screen. All 6 lines are correctly listed for the connections. So I see no issues with these two units at this time. Not sure why...battery wasn't fully charged up???  who knows WTF is going in but all is right at this time. 

My two NESTS that only a heating connection with a separate transformer providing power for the Rc and C both have the RH greyed out but shows a wire connected to it. They are charging at 200ma and working. One has a display model of 3.4 and one is 3.6. Both have no N errors displayed anymore on equipment screen. Working fine at this time. Maybe the greyed out RH will go away over time???  It works and I'm done screwing with it. Will never use or recommend NESTS to anyone I know...maybe enemies. Maybe it wants a W connector too in addition to my RC and C but I don't think I want to jumper the W and C together in the base unit. 

Chobes
Community Member

It sounds like they did an update. Not sure if it was related to fix our issue but if I remember correctly the issue started after an October update

Jpbone120
Community Member

Pretty sure we all uninstalled the nest and installed another thermostat lol

SofianeMTL
Community Member

I am about to change for the Ekobee

I stalled Ecobees in my sister's house and she loves them..... I would install them in mine if I had to do it all over...slightly cheaper and no issues with them other than they require a dedicated C wire but they also have an optional  conversion device you can use if needed.    I went for the fancy Nests and should have known better!

 

 

 

 

 

gp1200x
Community Member

I hope in the end there is a lawsuit against Google requiring them to buyback or refund money...I would probably swap them out...I hate the learning nest and disabled most of the functions...it really doesn't work that well in northeast winters

 

 

 

 well 

mmetz5
Community Member

So lots and lots of replies.  Quick update which I was waiting a while to make (probably about to jinx everything).

So spent a reasonable time on support with Nest/Google, after 1 disconnection and restart (ugh), I was able to get a replacement thermostat (no base) and although the wiring still is the same it has been a few months and still working without issue.  Still concerned however as Iast time Nest was installed in Oct and no issue till ~May following year.  We will see what happens as the months pass.

Ptook86
Community Member

So for everyone who is not sure where to start. Do a hard reset of your Nest (not the full erasing of settings but just a regular restart). I’ve had this happen a couple times (randomly) and after trying a bunch of stuff the reset worked. This issue can be overwhelming when you see people suggesting legitimate HVAC work. Do the reset first and go from there. 

Cip54
Community Member

I ‘ve had four nest (learning 3rd gen) for a couple of years. Recently 3 of them have been having issues powering down to “save battery”. They usually come back after a day or so.

the fourth is only heat and has had no problems. I live in MA and also have baseboard heat/forced air a/c. One unit is a/c only and is experiencing power issues too.

I don’t have C wires but didnt have a power problem until a few weeks ago. My dual heat/ac thermostats have had the n72 error since day one but it never made any difference. 

If I disconnect the Rc and Y wires the n72 error goes away, and my heat has always worked, so clearly the software is incorrect about not getting power on the heat side. I suspect it is trying the “jump” the Rh to the A/C side and of course it doesn’t work. It’s maddening that they still haven’t fixed this. Of course my a/c only unit is not affected by the n72 message but still loses power.

I’m installing a nest power adapter tomorrow, hoping it fixes the power issue. 

Just adding to the info…

Cip54
Community Member

quick update- installed the power adapter on one of my air handlers. Install was simple.

One thing to know- charge up the thermostat while you are installing the adapter. Mine ran low on power while the breaker was off and gave an incorrect "no power on Y1 error" in the app when I powered back up, causing me to scratch my head and rewire. With the Nest fully charged there was no error.

Bottom line, the Nest is now keeping a full charge and the A/C is running correctly. Both of my other A/C Nests are offline with low batteries. I'm going to let the system alone for a week, and if all still looks good will install the adapter on  the other 2 air handlers.

Finally, the Nest still reports an N72 error (Rh power not detected) but this does not seem to affect performance at all. I believe this is because I have a separate hot water baseboard system with a separate transformer.

Chobes
Community Member

The AC is not the issue. It’s unable to run the heat in the winter properly with the N72 error

Cip54
Community Member

I’ve never had any issues with heating in spite of that error.