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.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.