NEST Learning Thermostat Loss Of Power = Error E80

NEST Learning Thermostat Loss Of Power = Error E80

NEST Learning Thermostat Loss Of Power = Error E80


The main error I was getting was “No power to Y1 wire.”  I then lost Internet connection to the NEST because the NEST internal battery was not charging and it’s voltage went too low to maintain that connection.

The NEST Learning Thermostat needs 24 volts AC from the furnace unit.  The two wires that provide this power is Red marked Power and Y1.

Internet Source:   At this time, the Nest Learning Thermostat is only designed to work with 24Vac systems that are connected directly from the control board using solid copper wires.

I measured 24 volts on the Y1 Yellow wire and the Red power wire at the furnace unit wiring interface board.

I then went to the NEST and measured 24 volts with Yellow and Red pulled out of their connections.   I then took the Red wire and slid it in and out of it’s connector to clean it.  I did the same with the Y1 wire.  I should have used a pocket knife or some other sharp metal object to rub against the wires to clean them.  The UNIT WORKED as soon as I put the wires back in!  The NEST showed the problem to be the Y1 connection but actually it was the Red power wire that was not making a good connection.

We still showed a low battery but the system works.  This should not happen now that the unit is getting proper power.


  • A voltage of at least 3.7V is required to install a software update.
  • A voltage of 3.6V is required for the display to turn on when you approach.
  • The Nest Thermostat’s battery voltage will fluctuate.
  • But your voltage should generally be higher than 3.6V if everything is functioning normally.

I then went into the NEST menu and performed a Restart but specified that no saved settings be removed and the NEST came back showing no low battery!  Total success.


This repair worked for just over a year and then a new problem occurred.  The new problem was similar to the one described in this post.  The new problem was that the thermostat was receiving low power.  To view this next repair go to this web page:


Post updated: December 5, 2019

One thought on “NEST Learning Thermostat Loss Of Power = Error E80

  1. We are just now having the identical issue, now that our temp in KS is to drop!! We have space heaters going – our AC/heating guy smirked when we pulled this out of the box. (Our son had given this item to us as a gift a year ago). So, will clean the wires, and see if it works, so many thanks for your post. This better work, or back to Nest it goes!!!!

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