Carrier Furnace Troubleshooting: Error Codes, DIY Fixes & When to Call GSHA Services
If your Carrier furnace is flashing lights or throwing a thermostat fault, this guide explains what those codes mean, which safe checks you can try, and—crucially—when to schedule a professional repair. Consequently, you can get heat back quickly and safely.
How to find your Carrier furnace error code
- First, check the sight glass on the blower door for a flashing LED pattern. Carefully count short and long flashes (for example, 3 short + 3 long).
- Next, read the code chart printed on the inside of the blower door panel—it maps flash patterns to fault meanings for your model.
- Then, if you have an Infinity/Evolution system, tap Menu → Service → Faults on the wall control to read active and historical faults.
- Finally, if you’re unsure of your model, look for the model number on the rating label inside the furnace so you can open the exact owner’s manual online.
Quick checks most homeowners can do
- First, the thermostat: Set to Heat, then hold a temperature above room temp; if needed, replace batteries.
- Next, the air filter: Replace it if it’s dirty. Restricted airflow can overheat the furnace and, therefore, trigger codes.
- Then, vents/returns: Open and unblock supply registers and return grilles; otherwise, airflow suffers.
- Also, power & switch: Verify the furnace switch is ON and the breaker hasn’t tripped; if it has, reset once.
- Additionally, condensate drain (90% furnaces): Make sure the drain line and trap are clear and not frozen; consequently, the pressure switch can close properly.
- Meanwhile, intake/exhaust pipes: Outside terminations should be free of snow, leaves, or nests; afterward, recheck operation.
- Finally, the door switch: Ensure the blower door is fully seated to engage the safety switch.
If a code returns after these steps, book a professional diagnosis right away.
Common Carrier furnace problems & solutions
No heat or won’t start
Likely causes: Tripped breaker, door switch open, thermostat call not reaching furnace, pressure switch not closing, or ignition failure.
DIY checks: Power/breaker → thermostat settings/batteries → replace filter → verify intake/exhaust are clear. If it still won’t start, avoid repeated resets.
Pro fix: Diagnostic of control/pressure switch, inducer, gas valve, hot surface igniter, flame sensor, wiring, or board.
Short cycling (starts/stops quickly)
Likely causes: Dirty filter, blocked vents/returns, oversized system, or high‑limit trips.
DIY checks: Replace filter, open vents, and check airflow. Then, observe whether the furnace completes a full heat cycle.
Pro fix: Static pressure test, blower speed/CFM setup, duct repair, limit/rollout evaluation, or control board diagnosis.
Blower runs but air is cool
Likely causes: Ignition failure, gas supply issue, fouled flame sensor, or control lockout.
DIY checks: Replace filter and, after a power cycle, watch for the ignition sequence.
Pro fix: Clean/replace flame sensor or igniter, verify gas pressures, and test control relays/valve.
Water around the furnace (condensing models)
Likely causes: Clogged condensate trap/drain, cracked collector box, or frozen line.
DIY checks: Ensure the drain line/trap are clear and pitched; replace clogged tubing if accessible.
Pro fix: Flush trap, replace cracked components, and confirm furnace pitch.
Carrier error codes (what they usually mean)
Code names below are common across many Carrier models but can differ by series. Therefore, always confirm with your door chart/manual.
Airflow & Venting Codes (Overheating/Pressure)
These faults often trace back to airflow restriction or vent/drain issues. Consequently, start with filter and vent checks before moving to component tests.
| Code | Typical name | What it usually indicates | Safe homeowner actions | What GSHA checks/fixes |
|---|---|---|---|---|
| 33 | Limit Circuit Fault | High‑limit or rollout switch open; overheating/airflow issues. | Replace filter; open supply/return vents; check for blocked airflow. | Verify temperature rise; set blower speed/CFM; correct duct restrictions; replace faulty limit/rollout; investigate combustion/venting. |
| 31 | Pressure switch open/failed to close | Venting/condensate blockage, inducer or switch issue. | Replace filter; verify intake/exhaust and condensate are clear. | Manometer tests; inducer operation; pressure switch calibration; drain/vent cleaning or component replacement. |
| 13 | Limit Circuit Lockout | Furnace locked out after repeated high‑limit/rollout opens. | Power‑cycle once; then replace filter and open vents/returns. | Airflow diagnostics; verify temperature rise; inspect/replace limit/rollout switch; check blower speed, duct/static pressure; verify heat exchanger/venting. |
Ignition, Flame & Electrical Codes (Light‑off/Signal/Power)
When airflow looks good, these codes point to ignition, flame sensing, or control power problems. Accordingly, avoid repeated resets and schedule service.
| Code | Typical name | What it usually indicates | Safe homeowner actions | What GSHA checks/fixes |
|---|---|---|---|---|
| 14 | Ignition Lockout | Failed to light after retries. | Confirm gas is on; however, don’t keep cycling. | Test hot‑surface igniter and flame sensor; verify gas valve operation, manifold pressure, and control board timing. |
| 21/22 | Gas heat lockout / Abnormal flame proving | Flame signal out of range or unstable. | None beyond filter/power checks. | Clean/replace flame sensor; check ground/polarity; correct gas pressure, flame carryover, and burner alignment. |
| 23 | Pressure switch did not open | Stuck closed between cycles. | None beyond power cycle. | Check wiring, pressure tubing, switch calibration, and inducer relay/board. |
| 24 | Secondary voltage fuse open | 3‑ or 5‑amp low‑voltage fuse blew. | Inspect for visible thermostat‑wire shorts if accessible. | Find/repair shorted circuits (humidifier, outdoor unit, thermostat wiring); replace fuse; protect wiring. |
| 41 | Blower motor fault | ECM/PSC motor fault or wiring issue. | None beyond breaker/power checks. | Test motor module/capacitor, wiring, and control outputs; replace motor or board. |
| 42 | Inducer motor fault | Inducer not reaching speed or not proven. | Ensure vent/intake clear. | Test inducer motor/pressure proving; replace if needed. |
| 45 | Control circuitry lockout | Internal control fault or serial communication lockout. | Power‑cycle once only. | Board/communication diagnostics; repair/replace per test results. |
How to clear or reset a fault (safely)
- Momentary power cycle: Switch the furnace OFF for 30 seconds, then ON. If a safety fault returns, do not keep resetting—schedule service.
- Manual‑reset rollout/aux limits: Some models have red/black reset buttons near the burner area. If tripped, do not bypass. Reset once only and call for service to check for overheating or flame rollout.
- Infinity/Evolution controls: Fault history can be cleared from the thermostat after repairs. Nevertheless, the cause must be corrected first.
When to call GSHA Services
- If the same error returns after a reset or filter change—then deeper diagnostics are needed.
- If you see codes 13, 14, 31, 33, 41, 42, or 45, especially alongside repeated shutdowns.
- If there’s a gas smell, scorch marks, or tripped breakers—immediately turn the system off and contact us.
- Additionally, call if you notice water leaks, rusting, or corrosion inside the cabinet.
- Finally, if the furnace is short cycling or the breaker trips repeatedly, professional service is strongly recommended.
Preventive maintenance tips
- Replace the air filter every 1–3 months during heating season.
- Keep all vents and returns open for proper airflow.
- Clear intake/exhaust terminations each fall and after heavy snow.
- Have GSHA Services perform annual furnace tune‑ups to test safeties, sensors, gas pressures, temperature rise, and clean components.
FAQs
What does Carrier code 33 mean?
It usually means a limit circuit fault—the furnace overheated or a limit/rollout switch opened. Check airflow (filter/vents) and schedule service if it returns.
What does Carrier code 31 mean?
Typically a pressure switch or venting issue. Check the filter and ensure intake/exhaust and condensate are clear, then call for diagnosis.
Why does my furnace lock out?
Multiple failed ignition attempts or repeated safety trips place the control in lockout to protect your home. A technician must correct the root cause.
Can I keep running the furnace with a fault?
No—do not bypass safeties. If heat is needed, schedule priority service.
Service Area — Approximately 60 Miles Around ZIP 60098
We proudly serve Chicagoland and Southeast Wisconsin up to Milwaukee. The list below highlights many of the larger cities we cover; if you’re near the edge of the radius, please call to confirm.
Illinois
- Chicago (North/Northwest areas)
- Rockford
- Elgin
- Schaumburg
- Arlington Heights
- Naperville
- Aurora
- Waukegan
- Evanston
- Des Plaines
- Hoffman Estates
- Palatine
- Gurnee / Libertyville
- Lake Zurich / Barrington
- Crystal Lake / McHenry
Wisconsin
- Milwaukee (select areas)
- Waukesha
- Kenosha
- Racine
- Janesville
- Beloit
- Brookfield
- Lake Geneva
- Burlington
Contact Us for Furnace Repair
When you need an air conditioning repair in the Chicagoland area, GSHA Services, LTD is the place to call. No matter how unique your particular cooling system problem seems, including Carrier furnace troubleshooting, our highly skilled repair team has probably seen it before.
If you are without heat or air conditioning and need an emergency repair or installation, call 224-220-3660. We have professional field reps on-call 24 hours-a-day, 7 days-a-week. Whether it’s air conditioning or Carrier furnace troubleshooting, we’ve got you covered. For those experiencing issues with their Carrier furnaces, our troubleshooting guides can be invaluable. Especially for Carrier furnace troubleshooting, our team is ready to assist at any time.