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M20/E298 error but when test wires I have adequate voltage

BEinDC
Community Member

My Nest keeps disconnecting from Wifi and turning off because of M20 and E298 error messages. When I check the power information, it shows that voltage is fluctuating to the thermostat. However, when I use my multimeter to check the voltage to the thermostat it is steady at 24V. What gives? Is the thermostat defective?

7 REPLIES 7

Jenelyn_O
Community Specialist
Community Specialist

Hi BEinDC, 

 

Thanks for reaching out and for being a step ahead of us. 

 

The reason why the Nest Thermostat gives you that code if the common wire isn't properly grounded or a connection failure may be in one of the power terminals and causes the power loss. Could you please share your thermostat wiring?

 

You can check out this guide.

 

Regards,

Jenelyn

BEinDC
Community Member

Hi Jenelyn - thanks for following up. My house is older so it only has a R/W set up without a common wire. However, I'm confused why a common wire is required when the R/W is giving the thermostat 24V of consistent power per my multimeter. Is a common wire required irrespective?

Jenelyn_O
Community Specialist
Community Specialist

Hi BEinDC,

 

Thanks for getting back to us, I'm sorry for the confusion. Unlike other wires connected to your Nest Thermostat, a C wire doesn’t control heating or cooling functions. It only provides constant power to your thermostat to make sure that your thermostat will avoid any power issues. 

 

Instead of C wire you can install the Nest Power Connector as a substitute for C wire. 

 

You can check this link for additional information about Common wire and Nest Power Connector.

 

Best,

Jenelyn

EmersonB
Community Specialist
Community Specialist

Hi everyone,
 

@BEinDC I'm dropping by to ensure that everything is covered here. How's it going with your Nest Thermostat? Try giving these steps a try:

  • Turn off your switch breaker for your HVAC system.
  • Remove the display of your Nest Thermostat and pull off all the wires.
  • Make sure there is no damage or burnt.
  • Connect it back to their terminals and make sure they are connected properly.
  • Put the display back and turn on your switch breaker.
  • Try checking the power reading from your Nest Thermostat.
  • Hit this link for more information.

Looking forward to your response.
 

I appreciate the help, Jenelyn.
 

Regards,

Emerson

EmersonB
Community Specialist
Community Specialist

Hello BEinDC,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let us know.
 
Thanks,
Emerson

Jenelyn_O
Community Specialist
Community Specialist

Hi BEinDC,

 

I wanted to follow up and see if you still need help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

 

Best,

Jenelyn

Jenelyn_O
Community Specialist
Community Specialist

Hi BEinDC,

 

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this thread in 24 hours.

 

Best,

Jenelyn