Showing results for 
Search instead for 
Did you mean: 
Replies are disabled for this topic. Start a new one or visit our Help Center.

Nest E72 error

Community Member











Neat thermostat is intermittently getting E72 error like others. I continue to do resets. It’ll go weeks without the error and other times it’ll go to error every time I reset it. Help!  It’s hot as hell in my house. 


Community Specialist
Community Specialist

Hello KendraMS,

Thanks for reaching out to the Google Nest Community Forum. I'd be happy to take a look at this for you.

A connection failure may be in one of the power terminals and cause the power loss. To isolate:


  1. Make sure that the breakers are on.
  2. Ensure that all wires are properly connected.
  3. Check the air filter.
    1. A clog in the air filter can limit how much air flows over the cooling coils. If the clog persists, the cooling coils can freeze and cause the system to shut off.
  4. Check the emergency switch.
    1. This will not be the same as the breakers on the fuse box. This will be a breaker right next to the furnace or boiler. It might be a light switch, a breaker, or a T switch (you will need to unplug and plug back in the T switch). If anything went wrong electrically (like a power outage), this breaker should be the one to go off, so you may try turning it off and back on.
  5. Check the drip pan.
    1. This would be located on the AC unit, not the heating. You may need to open a door or take the cover off. There should be a pan with water inside. If there is any water, it must be drained or vacuumed.
    2. If the AC unit has drain pipes instead of a drip pan, the water will drain by itself.
  6. Consider hot weather as a factor in power loss.
    1. Check the energy-saving box. Some utility companies install boxes that cut off the power during high-demand (peak) times. These energy-saving boxes can cause the error.
  7. Check the condition of the HVAC fuse. Occasionally, fuses burn out due to one or more reasons.


Let us know how it goes.




We, also, are having this problem.  Stated today.  My husband has checked the wiring a few times & all seems intact.  He turned the breaker of & back on a couple of times.  He initially pulled out the RH wire & cleaned it off & reinserted it.  That seemed to correct the problem for 1-2 hours.  Now that the same is happening, he cannot get it to start up again.  At 1 point it gave a message of a low battery & said the system needed to shut down for us to replace/recharge the batteries.  At that point, we charged with usb, but after only 5 minutes, the display gave message to connect it back to the thermostat base.  Needless to say, that didn’t work for us.  Our system is not running at this time.  The app shows it’s  Offline, and it doesn’t have enough power to connect to WiFi.  In the meantime, we’re located in Southwest Florida, and it’s starting to get warm in here.  Please help.

Community Specialist
Community Specialist

Hi PP628510,


Oh no! I appreciate you posting on this thread and for taking a series of steps. I'd love to know more about your Nest Thermostat and HVAC system.


  • Gather its power readings in the Technical Info option (Voc, Vin, Lin).
  • Does your thermostat have a C wire connected?
    • If it has, remove the C wire and leave it disconnected.
  • Press and hold the thermostat screen for 10 seconds until it shuts down to refresh.
    • If the battery is low, charge the display for an hour before plugging it back into its base.
  • Were there any recent power outages that occurred?
  • Have you tried checking the steps I shared above?


Note: Turn off the power from your HVAC system at the breaker box before touching a wire.

Keep me posted.