Error code No C power

[Gsan1124]

Hi, I have had my nest thermostat's 2nd generation installed for 10 years now & never had any issues. Suddenly 2 days ago 1 of my nest thermostat is reading No power to c wire E29 error code. My c wire is & has been connected & nothing has been touched or moved or replaced. What is goin on all of a sudden? 
I have 4 zone Taco & 3 thermostats. 
The e29 code is thermostat that controls HVAC the other 2 heat only. 
I swapped thermostats to check if unit was bad, but still have same issue. 

[moralesvicente · Accepted solution]

Hey  Gsan1124

Don’t worry I’m here to help you, Here’s some information on troubleshooting thermostat nest help codes

Regarding this error code E29, please remember to check: 

• The system power( take a look of your HVAC system is having power) 
• The thermostat wires (if the thermostat wires are all properly connected and the C wire is receiving enough power)

If the inconvenience  continues, my best advice is to contact one of our partner technicians for professional help.

Regards

Daniel

[Gsan1124]

Hi, I have had my nest thermostat's 2nd generation installed for years now & never had any issues. Suddenly a few days ago 1 of my nest thermostat is reading No power to c wire E29 error code. My c wire is & has been connected & nothing has been touched or moved or replaced. What is goin on all of a sudden? 
I have a 4 zone Taco & 3 thermostats, Zone 2 is the one that is not functioning which is the HVAC system, the other 2 thermostats are working

What can I move around or switch? Each zone has 2 wires on the Taco box so I’m a little confused