Quick answer: Carrier code 31 (three long flashes, one short) means the pressure switch did not close or reopened during the heating cycle. The inducer fan has to prove the exhaust is flowing before the gas valve opens. In Illinois winters, the most common causes are snow or frost blocking the PVC vent pipes, a clogged condensate trap, a cracked or water-filled pressure switch hose, or a weak inducer motor. Bryant and Payne furnaces use the same code.
Safety first: if you smell gas, do not reset or relight anything. Leave the home and call your gas utility (Nicor Gas 1-888-642-6748, or North Shore Gas 1-866-556-6005) or 911 from outside.
Why Code 31 Happens
When your thermostat calls for heat, the inducer motor starts and pulls air through the heat exchanger and out the vent. That draft pulls a small diaphragm in the pressure switch closed. If the switch never closes, or opens again during the cycle, the control board shuts the gas off and flashes 31. It is a safety shutdown that keeps exhaust gases from building up in the furnace.
Common Causes of Code 31
- Blocked intake or exhaust pipe. Snowdrifts, ice rings at the pipe ends, bird nests or leaves.
- Clogged condensate trap or drain. On 90%+ furnaces, water backs up into the inducer housing and the switch cannot close.
- Cracked, kinked or water-filled hose between the inducer and the switch.
- Weak or failing inducer motor that cannot create enough draft.
- A failed pressure switch. Less common than the causes above, and the one most often replaced unnecessarily.
- Vent pipe problems such as a sag that holds water or a run that is too long.
Safe Checks You Can Do
- Go outside and clear the two white PVC pipes. Remove snow and ice gently by hand. Do not chip at the pipe.
- Check the condensate drain. If you have a condensate pump, make sure it is plugged in and not full.
- Listen for the inducer. If it runs but the code still appears, the problem is usually the hose, trap or switch.
- Reset power once. If code 31 returns, call for service.
What a Technician Checks
We measure the draft the inducer is producing with a manometer and compare it with the switch rating, inspect and blow out the hose and ports, clean the condensate trap, and check the venting. That tells us whether the switch is bad or simply reporting a real venting problem.
What Code 31 Repairs Cost
| Repair | Flat-rate price |
|---|---|
| High-efficiency condensate trap cleaning or replacement | $290 |
| Pressure switch hose replacement | $250 |
| Pressure switch replacement | $355 |
| Flue or PVC vent pipe repair | $435 |
| Inducer motor replacement | $570 to $1,410 |
Prices are flat-rate with parts and labor, as of November 2026. The $75 diagnostic is waived when you approve the repair, and Comfort Club members save 10 to 15% on repairs. Exact pricing depends on your furnace model and whether the part is in stock on our trucks.
Seeing a Carrier code in the Northwest Suburbs?
Pure Comfort Heating and Cooling services every major furnace brand from our shop in Streamwood, IL. Diagnostics are $75, or $99 on evenings, weekends and holidays, and the fee is waived when you approve the repair. You approve a flat-rate price before any work starts, and phones are answered 24/7.
Other Error Code Guides
- Furnace blinking light codes by brand
- Lennox furnace error codes
- Carrier, Bryant and Payne furnace codes
- Goodman, Amana and Daikin flash codes
- Trane and American Standard blink codes
- Furnace pressure switch errors
Frequently Asked Questions
Can I clear Carrier code 31 myself?
Often, if the cause is snow or ice blocking the vent pipes outside. Clear them, reset power once, and if the code comes back, call for service.
Is code 31 dangerous?
The code itself is a safety shutdown, so the furnace will not run unsafely. Do not bypass the pressure switch, because that can let exhaust gases back into the home.
What is the difference between code 31 and 32?
On two-stage furnaces, 31 is the high-heat pressure switch and 32 is the low-heat pressure switch. The causes are the same.
Why does code 31 happen more in winter?
Snow and ice block vent pipes, condensate lines can freeze, and furnaces run longer, which exposes weak inducers and clogged traps.
We diagnose and repair furnaces from our shop in Streamwood across Streamwood, Bartlett, Hoffman Estates, Schaumburg, Elgin, Hanover Park, Roselle, Arlington Heights and the rest of the Northwest and West Suburbs. See our furnace repair page for flat-rate prices.