Bryant Furnace Code 13 Limit Switch Lockout Troubleshooting Guide

This article explains what a Bryant furnace code 13 means, why the furnace goes into a limit switch lockout, and practical diagnostic and repair steps for homeowners and HVAC technicians. It focuses on safety, common causes, step-by-step troubleshooting, and prevention to help restore reliable operation.

Item	Quick Summary
Code	13 — Limit Switch Lockout (high limit reached / repeated trips)
Likely Causes	Restricted airflow, dirty filters, closed vents, faulty inducer, stuck or failed limit switch
Immediate Actions	Turn off furnace power, check filter and vents, reset per manual, inspect for overheating
When To Call A Pro	Repeated lockouts, electrical/heat exchanger concerns, failed component replacement

What “Code 13 Limit Lockout” Means

On many Bryant furnaces, Code 13 indicates the high-temperature limit switch has tripped repeatedly or the control board has detected a limit-related lockout condition. The limit switch is a safety device that prevents overheating by cutting gas and ignition circuits when temperatures exceed safe thresholds.

When the control board sees multiple limit trips or a persistent overtemperature condition, it records Code 13 and places the furnace in lockout to prevent unsafe operation until the underlying issue is resolved.

How The Limit Switch Works

The limit switch monitors plenum or heat exchanger temperature. When airflow or combustion problems cause temperatures to rise above the setpoint, the switch opens and interrupts the burner and inducer sequence.

Some systems use multiple thermal sensors (rollouts, high-limit, flue sensors). A repeated open condition signals the control board to log a lockout code and disable normal cycling until reset.

Primary Causes Of Code 13

Several factors commonly trigger a limit switch trip; address these in order from simplest to most complex:

• Restricted Airflow — Dirty filters, blocked return vents, closed supply registers, or dirty evaporator coils reduce airflow and raise temperatures.
• Blower Problems — Malfunctioning blower motor, capacitor failure, or belt slipping reduce airflow through the heat exchanger.
• Inducer Or Venting Issues — Poor combustion air or clogged venting increases combustion temperatures and can trigger safeties.
• Faulty Limit Switch — A mechanically or electrically failed limit switch can trip prematurely or fail to reset.
• Control Board Or Wiring Faults — Short circuits, corroded connections, or board malfunctions may report spurious limit conditions.
• Heat Exchanger Or Gas Valve Issues — Incomplete combustion or burner problems that cause overheating.

Safety First: Immediate Steps When Code 13 Appears

When Code 13 appears, follow safety precautions before troubleshooting further:

• Turn off power to the furnace at the service switch or breaker to prevent accidental restarts.
• Shut off the gas supply if any burning smell, visible flame irregularities, or suspected heat exchanger damage exists.
• Do not attempt to operate the furnace continuously while the cause of the limit trip is unknown.

Basic Homeowner Troubleshooting Checklist

Homeowners can perform non-invasive checks to resolve common causes. Each step is safe and quick.

1. Replace Or Clean The Air Filter — Use the correct size and MERV rating. A clogged filter is the single most common cause of overheating.
2. Inspect Supply And Return Vents — Ensure registers are open and furniture or curtains are not blocking airflow.
3. Check The Blower Area — Ensure nothing obstructs the blower compartment and the fan turns freely if accessible.
4. Reset The Furnace — Follow the owner’s manual reset procedure or cycle power at the service switch after correcting airflow issues.
5. Confirm Venting Is Clear — Check outside vent terminals for bird nests, snow, or debris that may obstruct exhaust or intake pipes.

Diagnostic Steps For Technicians

Technicians should follow a systematic approach combining visual inspection, measurements, and component tests to pinpoint the root cause of Code 13.

• Control Board Logs — Read stored error history and observe LED flash patterns to confirm the exact lockout cause and sequence.
• Airflow Measurement — Measure static pressure across the filter and coil and compare to manufacturer specifications.
• Thermostat And Sequence Checks — Verify proper call for heat and confirm inducer and ignition sequence timing with a multimeter or combustion analyzer.
• Limit Switch Testing — Test continuity of limit and rollout sensors at room temperature and during controlled run to see if they open at proper setpoints.
• Blower Amp Draw — Check blower motor amperage against nameplate to detect motor or capacitor issues.
• Combustion And Venting — Inspect burners, flame pattern, and flue gases to rule out combustion irregularities causing excessive temperatures.
• Heat Exchanger Inspection — Visual inspection for cracks, corrosion, or signs of overheating. Cracked exchangers warrant immediate service and possible shutdown.

How To Test And Replace A Limit Switch

Technicians typically perform these steps to test or replace a limit switch safely:

1. Power Down The Furnace — Cut electrical power at the breaker and shut off gas supply to avoid ignition while working.
2. Access The Switch — Remove the blower or access panel to reach the limit switch mounted on the plenum or heat exchanger housing.
3. Test For Continuity — Use a multimeter to test continuity across the switch at room temperature. A normally closed limit should show continuity until it trips.
4. Simulate Trip Safely — Heat the switch gently with controlled means (if recommended by manufacturer) to confirm it opens at the proper temperature or replace if uncertain.
5. Replace With OEM Spec — Use manufacturer-specified replacement parts and match temperature ratings and connector types.
6. Reassemble And Test — Restore power and perform a full sequence test, monitoring temperatures and ensuring no immediate retrips.

When To Replace Components Versus Repairing

Decisions to replace or repair should consider safety, cost, and long-term reliability:

• Replace the air filter, blower capacitor, or vents when performance issues are minor and parts are inexpensive.
• Replace the limit switch if it shows inconsistent continuity or fails to reset; limit switches are safety devices and should not be tampered with.
• Replace the control board only after ruling out wiring faults and validating that sensors are functioning; boards can be costly and sensitive.
• If the heat exchanger is cracked or severely corroded, discontinue operation and consult a licensed technician; replacement or system retirement may be necessary.

Preventive Maintenance To Avoid Future Lockouts

Regular maintenance minimizes the risk of Code 13 events and prolongs system life:

• Change filters every 1–3 months or per manufacturer guidance.
• Schedule annual professional tune-ups to inspect burners, heat exchanger, blower motor, and controls.
• Keep return registers and ductwork clean and unobstructed.
• Install a carbon monoxide detector and ensure vents remain clear of obstructions year-round.

Cost Considerations And Typical Repair Times

Costs and time vary by issue severity. Typical ranges in the United States include:

Repair Item	Typical Cost Range	Time To Repair
Air Filter Replacement	$5–$60	10–30 Minutes
Limit Switch Replacement	$50–$200 Parts+Labor	30–90 Minutes
Blower Motor/Capacitor	$150–$600	1–3 Hours
Control Board Replacement	$200–$800	1–2 Hours
Heat Exchanger Replacement	$1,200–$3,500 Or More	Several Hours To Full Day

When To Call A Licensed HVAC Technician

Code 13 outcomes often require professional attention for safe, durable repairs. Contact a licensed HVAC technician when:

• Repeated limit trips occur after basic airflow fixes.
• There are signs of flame instability, soot, or unusual odors.
• Heat exchanger damage or suspected carbon monoxide risk is present.
• Electrical troubleshooting beyond basic visual checks is necessary.

Common Manufacturer Recommendations And Warranty Notes

Follow Bryant/Carrier group guidelines for diagnostics, replacement parts, and control board procedures. Using non-OEM parts may affect warranty coverage and system performance.

Document all service actions and keep receipts for warranty claims. If the furnace is under manufacturer or installer warranty, consult the warranty terms before replacing major components.

Key Troubleshooting Flowchart (Summary)

Step	Action
1	Power off and inspect filter/vents
2	Replace filter, open closed registers, clear vents
3	Reset furnace and monitor for immediate retrip
4	If retrips, inspect blower, measure airflow/static pressure
5	Test limit switches, wiring, and control board logs
6	If heat exchanger or combustion concerns, stop use and call technician

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Additional Resources And Where To Find Parts

Official Bryant/Carrier documentation, furnace service manuals, and manufacturer wiring diagrams are primary resources for accurate testing procedures and replacement part numbers.

Replacement parts are available from authorized distributors, HVAC wholesalers, and reputable online retailers. Verify OEM numbers and consult local codes when replacing major components like heat exchangers or control boards.

Final Practical Tips

After addressing the root cause, monitor the furnace through several heat cycles to ensure no repeat lockouts. Keep a maintenance log noting filter changes, service visits, and any code occurrences.

For safety-critical failures such as cracked heat exchangers or repeated limit trips despite normal airflow, discontinue use and contact a licensed HVAC professional immediately.