Bryant Furnace Code 31 Meaning Troubleshooting and Fixes

The Bryant Furnace Code 31 often appears as a blinking LED or digital fault code and signals a safety or ignition-related problem that requires prompt troubleshooting. This guide explains what Code 31 commonly indicates across Bryant models, step-by-step diagnostics, likely causes, and recommended repairs to restore safe operation.

Issue	Typical Significance	Common Fixes
Code 31	Ignition/safety fault or limit/pressure circuit problem (varies by model)	Check error history, inspect venting, pressure switch, limit switches, flame sensor, control board, and gas supply; call technician if needed

What The Code 31 Indicator Usually Means

Bryant furnaces use a diagnostic LED or control display to report faults. Code 31 commonly points to an ignition or safety circuit issue, but the precise meaning varies by model and control board. It often indicates a protective limit triggered, a failed pressure switch, repeated ignition attempts without stable flame, or a control board detecting an unsafe condition.

Why The Exact Meaning Varies By Model

Different Bryant/Carrier control boards map numeric codes differently. The same “Code 31” can mean slightly different things on older versus newer models. Always verify the furnace’s data plate and owner’s manual or service sheet for the accurate code table for that specific model.

Safety First: Precautions Before Troubleshooting

Working on gas appliances involves risk. Turn off power and gas to the furnace before opening panels. If there is any gas odor, evacuate the home and contact the gas company or a qualified technician immediately. When in doubt, call a licensed HVAC technician to avoid personal injury or appliance damage.

Tools And Materials Needed For Basic Troubleshooting

• Multimeter for voltage and continuity checks
• Manometer or manometer adapter to test pressure switch and venting (optional)
• Screwdrivers and nut drivers
• Soft brush and emery cloth for cleaning flame sensor
• Replacement parts if required (pressure switch, flame sensor, limit switch, control board) — only if qualified to replace

Step-By-Step Troubleshooting Procedure

1. Record The Exact Behavior

Note how the code displays (steady blink vs flashes), when it appears (on call for heat, during ignition), and any sounds (clicking, continuous blower). This information helps pinpoint the stage where the system fails.

2. Check Error History And Model Documentation

Locate the model and serial number on the furnace data plate and consult the manufacturer’s service manual or tech sheet inside the access panel. Confirm the exact definition of Code 31 for that control board.

3. Inspect Venting And Airflow

Blocked or restricted venting can cause pressure switch trips and limit faults. Inspect intake and exhaust terminations outside for debris, bird nests, snow, or nearby obstructions. Verify flue pipe joints are secure and unobstructed.

4. Check Pressure Switch And Tubing

Examine the small rubber tubing connected to the pressure switch for cracks, blockages, or disconnection. Use a manometer or a multimeter continuity technique during a heat call to confirm the switch closes at the proper draft conditions.

5. Inspect Limit Switches And Rollout Switches

High-limit or rollout switches open to prevent overheating or unsafe combustion. Inspect for tripped switches and test continuity with a multimeter. A persistent open limit may indicate blower dysfunction, blocked return ducts, or a failing heat exchanger causing abnormal temperatures.

6. Evaluate Ignition And Flame Detection Components

If Code 31 corresponds to ignition failure on the model, inspect the flame sensor and ignitor. Clean the flame sensor gently with emery cloth and check the ignitor for cracks. Use a multimeter to verify resistance values if applicable.

7. Verify Gas Supply And Valve Operation

Confirm the gas shutoff is open and that other gas appliances operate. A faulty gas valve or inadequate gas pressure can prevent ignition. Gas valve diagnostics should be performed by a qualified technician.

8. Examine The Control Board And Wiring

Look for loose, corroded, or burned connectors on the control board. Faulty wiring or a compromised control board can produce false faults. Replace the control board only after confirming other components are functional.

9. Reset Procedure And Observation

After resolving visible issues, restore power and gas. Follow the furnace reset procedure indicated by the manufacturer. Observe multiple heat cycles to ensure the fault does not recur.

Common Causes Of Code 31 And How To Address Them

Cause	Symptoms	Diagnostic Actions	Typical Fix
Blocked Vent/Flue	Code appears during ignition; poor draft	Inspect outside terminations and vent piping	Clear obstruction; repair piping
Faulty Pressure Switch Or Tubing	Pressure switch doesn’t close; ignition stops	Check tubing, test switch with manometer	Replace tubing or pressure switch
Open Limit Or Rollout Switch	System shuts off during run; overheats	Test switch continuity; inspect airflow	Replace switch; fix airflow or fan
Ignitor Or Flame Sensor Problems	Ignition attempts but no stable flame	Inspect/clean sensor; test ignitor resistance	Clean sensor; replace ignitor or sensor
Gas Supply Or Valve Fault	No gas flow; repeated ignition attempts	Check gas pressure and valve operation	Repair gas supply or replace valve (pro only)
Control Board Or Wiring Fault	Intermittent or unexplained errors	Inspect connectors, test relays and outputs	Repair wiring or replace control board

When To Call A Professional HVAC Technician

If basic checks (venting, pressure tubing, flame sensor cleaning) do not clear Code 31, a licensed technician should be called. Gas valve replacement, control board diagnostics, and heat exchanger inspection require professional training and certification.

Preventive Maintenance To Reduce Code 31 Occurrences

• Schedule annual professional furnace inspection and tune-up before heating season.
• Keep outdoor vent terminations clear year-round.
• Replace air filters regularly to maintain proper airflow.
• Have combustion analysis and gas pressure checks performed periodically.
• Address unusual odors, noises, or performance drops promptly.

Estimated Costs For Common Repairs

Costs vary by region and specific model. Typical ranges: flame sensor replacement $75–$200, pressure switch $100–$250, limit or rollout switch $75–$200, ignitor $150–$350, control board $300–$800, gas valve $300–$700. Labor and diagnostic fees vary.

Recordkeeping And Reporting For Future Troubleshooting

Keep a log of fault codes, dates, repairs performed, and service provider notes. This history helps technicians identify recurring issues and supports warranty claims if applicable.

How To Find The Correct Bryant Code Definition For A Specific Furnace

Locate the model number on the furnace data plate and search the Bryant or Carrier online literature portal for the tech sheet. Many manuals include an LED code table that defines each numeric code for that control board. If the manual is not available, save the furnace model and contact Bryant/Carrier customer support or a dealer for precise definitions.

Key Takeaways

Code 31 Is A Diagnostic Flag, Not An Automatic Fix: It commonly indicates an ignition or safety circuit concern, but exact meaning depends on the control board. Prompt inspection of venting, pressure switch, limit switches, flame detection, gas supply, and wiring is essential. Simple actions such as clearing vents or cleaning the flame sensor can resolve many cases, but complex problems and gas-related repairs require a licensed technician.

For persistent Code 31 faults, follow the manufacturer’s guidance and consult an HVAC professional to ensure safe, reliable furnace operation.