02-08-2025 07:16 PM
I have been having difficulty installing this thermostat on an International Comfort Products forced air gas furnace model #NBF100F20G1 furnace with Honeywell controller boards and an A/C cooling unit. It works fine with a Honeywell Pro 2000 series thermostat. The G, Y, W and R/RC wires were connected (R and RC wires were jumped) in the Honeywell thermostat. I carried these connections over to the Nest unit. R wire shows 27 volts from the controller board on my multimeter.
Problem #1 - Nest display was dead. No green light when display was snapped onto the base
with wires connected and furnace plugged in . I plugged the display into a USB charger for a few hours, and it came to life.
Problem #2 - After setup, which all went well, the heating test failed. Furnace fan came on, but igniter did not light the gas. It keeps cycling with the fire box fan on and the igniter coming on, but the gas jets do not light. They may well not be on.
All wire connections are solid. Not sure what else to do. Any advice would be very much appreciated.
02-11-2025 12:00 AM
Can you post a picture of the original thermostat's wiring here if you have it?
Post a picture of the Nest wiring too.
02-12-2025 10:26 AM
02-12-2025 10:35 AM
Terminal labels from left to right are:
B O G Y W (1 not used) R RC
R and RC are jumped together.
G Y W and R/RC are connected.
I just connected the Nest thermostat to GYW and R. Don’t have a picture as it’s back in the box.
02-14-2025 01:13 PM - edited 02-14-2025 01:15 PM
The first possible problem I see is that network data cabling was used for the thermostat wiring, which is only 24 AWG. The Nest requires solid wires between 18 and 22 AWG (the larger the number, the smaller the wire). This can cause an intermittent connection between the wires and the Nest terminals. If possible, I would suggest replacing that cable with an 18/5 Brown Solid Copper CL2R Thermostat Wire.
The problems you describe can also be caused by the lack of a C-wire. If a spare wire is available, try adding one.