Gen4 e402 error

[Lchernov]

Hey all

I have a navien nhb150 with a zone controller and on it is 2 terminals for w1 and rh but the zone controller doesnt give power so i had to use a transformer for c and rc to power it up. It worked for 2 weeks and now i keep getting a e402 no r wire detected. Tried hooking up my gen3 nest and it works with the same woring config. If anyone know what can be the problem please let me know.

Thank you

[SoriaD_]

Hello @Lchernov 

Thanks for reaching out to our Nest Community. Apologize for all the inconvenience. Don't worry, I'm here to help you with this E402 error on your Nest Thermostat.

I completely understand this situation. Let me lend you a hand to find the solution. 

Can you please find the cooling coils in your HVAC system? Refer to your heat pump or AC manual for specific guidance on the location of the drip pan and drain tubes. Please avoid removing any sealed panels, as this might interfere with the system's operation. 

Once you've located the cooling coils, please check if there's any water accumulated in the drip pan, which is typically located beneath them. Examine the drain tubes for any signs of clogs. These tubes usually run from the AC unit to a drain or outside your home and are typically located on the side of the furnace. 

If you find water in the drip pan or drain tubes, please check for any signs of water damage or rust. You can either consult your HVAC system's user guide, search online for instructions on clearing a clog, or contact a professional technician.

Feel free to keep us posting if your situation persists; I will find a solution for you.

Best regards,

Douglas.