E188 OB wire error

[Amalander]

We have had our nest for over 5 years and today we got an E188 error saying our OB wire needs to be replaced. I’ve checked the breaker box switch and the wire break in the nest and both were on. When I reset the breakers, the AC will kick back on for 15 seconds and then turn off again with the error re-appearing. 

[Markjosephp]

Hello Amalander,

Thank you for taking the time to let us know about your inquiry. I'd be happy to take a look at this for you.

It appears that the thermostat's O/B terminal has an overcurrent or overvoltage problem (too much power is flowing through the thermostat). This report indicates that there have been repeated spikes in the electrical current on the thermostat wire leading to the Nest Thermostat, resulting in the activation of the thermostat's internal breakers to safeguard the thermostat base plate and other system components from harm.

Could you please gather its power readouts in the Technical Info settings with and without the O/B wire connected? Turn off the power from your HVAC system at the breaker before touching the wire.

Keep me posted.

Regards,
Mark

[Markjosephp]

Hey there,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Markjosephp]

Hi Amalander,

I'm checking in to make sure that you've seen my response. Please let us know if you have any additional questions or concerns before we close this thread in 24 hours. 

Best regards,

Mark