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

[BEinDC]

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?

[Jenelyn_O]

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]

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]

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]

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]

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]

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]

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