E23 Error after years of usage

[axiomer]

I have used this Thermostat for years and suddenly it displays E23 error and can’t control AC and Heater anymore. 

I checked according to official guide from google nest. And confirmed that Fuse is okay and there is no sensor issue.

What esle I can do more??

 

 

[Ianpinto]

I got the same issue after years of use and everything I see says to flush the drain and HVAC float switch … I got mine to come back on but I think my float switch might be damaged