11-29-2023 07:40 PM
Hi Folks, I recently acquired a Nest thermostat to replace my existing Honeywell model #THX9421R02 that has two wires labeled R and C and when I connect the NEST unit using the connection labeled R and C I receive an error message stating that it needs to be corrected via W and Y and when I make the chang I receive another error message stating that the voltage is low. As a consequence I am seeking assistance on how to address this issue. Ane whether the NEST is a suitable replacement for the Honeywell unit. All replies and suggestions will be greatly appreciated. @Link to members
11-29-2023 09:10 PM
The Honeywell THX9421R02 and Nest thermostat have some differences, notably in the wiring. For your specific setup, try connecting the Nest thermostat with the following wires:
- C: Common wire
- R: Power wire
- W: Heating wire
You can leave the Y wire unconnected since the Nest thermostat doesn't use it.
Regarding the low voltage error, it's crucial to ensure a secure connection of the C and R wires to both the Nest thermostat and your HVAC system. Also, check the voltage at the R and C terminals at the HVAC system; it should ideally be between 24 and 28 volts AC.
If, after these checks, the issue persists, I recommend getting in touch with a qualified HVAC technician for further assistance. They can provide on-site support to troubleshoot the problem.
Now, regarding whether the Nest thermostat is a suitable replacement for your Honeywell unit — absolutely! The Nest thermostat comes with some fantastic features, including a learning algorithm to adapt to your habits, a convenient remote control app, and a self-diagnosing system for troubleshooting.
12-03-2023 10:17 AM - edited 12-03-2023 10:26 AM
Hi Owhitedevil0, thanks for your response to my inquiry it is greatly appreciated, however I have a follow-up question. I have attached a photo of both my existing baseplate wiring and the NEST baseplate. I will be extremely grateful if you could provide me with a sketch showing how the NEST baseplate should be wired. A timely response will be greatly appreciated.
12-03-2023 11:15 PM
I understand. Based on the image you sent, your baseplate wiring only has two wires: R and C. This means that you have a single-stage heating system.
The Nest thermostat is a multi-stage thermostat, so it will not be compatible with your existing wiring.
If you want to use a Nest thermostat, you will need to upgrade your wiring to include a W wire. This can be done by running a new wire from the Nest thermostat to your HVAC system.
Once you have upgraded your wiring, you can connect the Nest thermostat as follows:
If you are not comfortable upgrading your wiring yourself, you can contact a qualified HVAC technician to do it for you.
I hope this helps!
12-05-2023 01:00 PM
Hello Volcar21,
I'd like to jump in here and check if you've seen 0whitedevil0’s response. Let us know if you need more help by replying to this thread.
I appreciate the help, @0whitedevil0.
Best,
Edmond