e298 and M20 Error. No changes to wiring.

[Tjdiz]

Just happened today after working no issues for 3 years.  Says no power, can't connect to wifi. Battery is good, wiring is good.

[virnab]

Hi Tjdiz,

Thanks for reaching out to our community.

I’m sorry to hear that after 3 years of working without any inconvenience, your thermostat is saying no power and showing e298 and M20 error messages. I understand how frustrating it must be not being able to connect to your WiFi network, especially after checking the battery and wiring are in good condition. No worries, help is here.

Before I start further troubleshooting, let me ask you a few questions:

• Could you please confirm the model of your thermostat device?  You can use this help center article as reference: Nest thermostat technical specifications 
• What type of heating, ventilation, and air conditioning (HVAC) system do you have?
• Could you check on the breaker box to see if the breakers flipped?
• Do you have a pre-existing thermostat?

• Is your Google Home app updated?
• Have there been any recent changes to the network and/or equipment?
• Are any other devices experiencing issues with the Wi-Fi connection?
• What network do you currently use, 2.4 GHz or 5 GHz?
• How far away is the thermostat from the router?
• Is the heating, ventilation, and air conditioning (HVAC) switch turned on?

In the meantime, I recommend you try the following troubleshooting steps:

1. Make sure the power to the system is on. The power switch is usually in the breaker box, but in some homes, it's like a light switch near the HVAC equipment. There may be one or two switches: one for heat and another one for cool. Make sure the power is on for both, then check the thermostat.
2. Check the thermostat wires:

1. Remove the thermostat display.
2. Ensure that the wires are in the correct terminals.
3. Ensure that each wire has ⅜ inch (9.5 mm) of exposed wire.
4. Ensure that each wire is properly seated.
5. Turn on the power to the system, then check if the thermostat works.

If the inconvenience persists, please check the walls and ceiling of your HVAC system’s air filter. The air filter is usually behind a grate in the hallway. If the air filter seems dirty or there seems to be a clog, it is necessary to replace the filter with a new one. 

Thanks for your kind attention; I will be looking forward to hearing from you.

Best regards,

Virna

[Patrick_Caezza]

@Tjdiz 

The E298 and M20 error codes mean your Nest thermostat isn't receiving power from your HVAC unit and the wifi will be turned off to save battery power.

This can be caused by several factors.

1. The overflow drain is clogged causing the drain safety switch to trip.
2. The fuse on the control PCB in the furnace/air handler has blown.
3. If you change the filter, it might not be properly installed.
4. If you removed any covers they might not be correctly installed.

How do you have the thermostat wired?

Can you post a picture of the baseplate wiring here?

You should check Technical Info screen under the Settings menu. What you need to look at is in the Power sub-menu.

Google Nest Thermostat (2020)

with or without C wire

• Voc: 29 to 42V
• Vin: 29 to 42V
• lin: 200 to 385 mA

Verify that your thermostats levels are in the ranges listed