This part is out of stock right now, so it cannot be added to the cart.
Most home thermostats run on a 24 V control signal from a transformer. If your old part carries the CT31A number, checking its wiring terminals and system match helps keep your system running properly.
Specifications
- Part number: CT31A
- Brand: Honeywell
- Part type: Thermostat
- Dimensions: 3 x 1 x 5 in.
- Stages: No
- System: No
- System: gas, electric or heat pump, as listed
- Stages: heat and cool stages your system uses
- C wire: needed by some models, check yours
From the maker's and parts sellers' listings for this number. Compare them with the label on your old part.
What the Honeywell CT31A Thermostat Does
A thermostat acts as the control center for your HVAC equipment. It senses the room temperature and connects low-voltage circuits to tell your heating or cooling system when to run.
Most central systems use 24 V control signals to switch equipment on and off. Baseboard heaters use line voltage. Because 24 V systems and line voltage setups are not the same, matching the control voltage is critical.
Understanding the CT31A Specifications
Reviewing the listed specs confirms the physical size and operational details of the CT31A.
- dimensions: 3 x 1 x 5 in.
- stages: No
- system: No
Checking System Match and Compatibility
Before replacing a thermostat, verify how your heating and cooling equipment is set up. Different systems use different wiring configurations.
Pay attention to these three core factors when confirming a match for your setup:
- System: gas, electric or heat pump, as listed.
- Stages: heat and cool stages your system uses.
- C wire: needed by some models, check yours.
Safe Removal and Wiring Tips
A faulty thermostat may fail to signal your equipment or may read room temperatures incorrectly. Swapping low-voltage wiring is straightforward if you work step by step.
Always turn off power at the breaker or furnace switch first. Before you pull the old thermostat off the wall, take a photo of which wire goes to which letter terminal. Move wires one at a time to the same spots on the replacement unit so you do not lose track of connections.
Read your old part
- Look at the front cover, backplate, or inner label of your current unit to find the model number.
- Verify that the label explicitly displays CT31A.
- Check that your heating and cooling system matches the required system type and voltage.
- Compare your wiring letters to the terminals on the replacement unit before disconnecting.
When to call a pro
Hire a licensed HVAC technician for any step you are not sure you can do safely. If your system involves line voltage or you cannot identify your wiring, contact a professional.
Questions
What voltage does this thermostat use?
Most central systems use 24 V thermostats powered by a transformer. Baseboard heaters use line voltage instead, so check your system before changing parts.
Why should I take a photo of the wiring before removal?
Taking a photo first shows which wire connects to which letter terminal. Moving wires one at a time to the matching spots prevents incorrect connections.
Do I need to turn off power before changing thermostat wires?
Yes. Shut off the furnace or air handler at its switch or breaker before touching any wires. Always test for power before you begin.
Does every thermostat need a C wire?
A C wire is needed by some models, but not all. Check your current setup and replacement requirements to see if one is needed.
Related part numbers
- CT87K1004Thermostat, HoneywellSame brand and type
- C7189U1005Thermostat Part, HoneywellSame brand and type
- 1053-00003-00Thermostat, FetcoSame part type
- 46910700Thermostat Specs and Replacement Guide, APWSame part type
- 1053-00004-00Thermostat, FetcoSame part type
- 370736Thermostat Export Fusion, LincolnSame part type
Browse: Thermostats by part number
All part numbers · Part number replacements · Shop thermostats · Repair guides
Brand names and part numbers identify the part and show fit. HVAC Fitter is not affiliated with, authorized by, or endorsed by any equipment maker. If you are not sure a repair is safe for you, call a licensed HVAC technician.