Goodman Furnace High Limit Switch Open: Causes and Repairs

The high limit switch on a Goodman furnace that remains open prevents the burner from running and can cause no-heat calls or frequent short cycling. This article explains why a Goodman furnace high limit switch opens, how to diagnose the issue safely, and practical repair and maintenance options to restore reliable heating.

Symptom	Common Causes	Typical Fix
Furnace Won’t Run (No Heat)	Open High Limit, Flame Rollout, Blower Failure	Reset/Replace Limit, Clear Venting, Repair Blower
Short Cycling	Overheating Due To Restricted Airflow	Clean Filter, Fix Blower, Check Ductwork
Intermittent Operation	Loose Wiring Or Faulty Sensor	Tighten/Replace Wiring, Replace Switch

What The High Limit Switch Does On A Goodman Furnace

The high limit switch monitors furnace cabinet temperature and prevents overheating by opening the electrical circuit to the gas valve or control board when temperatures exceed a safe threshold. On Goodman furnaces, it often acts as a primary safety device and a control input to the inducer or blower logic.

If The Limit Switch Is Open, the burner will be locked out until the temperature drops and the switch resets (if it is automatic) or until a manual reset is performed. Persistent open conditions indicate an underlying problem, not just the switch itself.

Common Causes For A Goodman Furnace High Limit Switch To Be Open

Restricted Airflow

Restricted airflow is the most common cause of overheating and an open high limit switch. Dirty filters, closed supply or return vents, blocked ducts, or a failing blower reduce heat transfer and raise cabinet temperature.

Blower Motor Or Capacitor Problems

If the blower motor isn’t running at the correct speed due to a bad capacitor, worn motor bearings, or electrical issues, airflow drops and the furnace overheats. This often triggers the high limit switch to open.

Dirty Heat Exchanger Or Burner Assembly

A soiled heat exchanger or obstructed burners can cause uneven combustion and higher localized temperatures. Scaling, rust, or soot buildup increases surface temperatures and can trip the limit switch.

Blocked Venting Or Flue Issues

Improper venting or partial blockage of the flue restricts exhaust flow and can cause the cabinet to heat up. This is especially relevant for sealed combustion units where ventilation balance matters.

Faulty Or Loose Wiring And Connections

Electrical faults including corroded terminals, loose spade connectors, or broken wires may make the control see the limit as open even if the sensor is fine. Intermittent wiring faults can cause erratic behavior.

Failing High Limit Switch

Like any mechanical or electro-mechanical device, the limit switch can fail open due to internal contacts wearing out or corrosion. Age, cycling frequency, and environmental conditions affect its lifespan.

Control Board Or Relay Problems

Some Goodman furnace control boards interpret limit inputs and route power through relays. A malfunctioning control board can display an open-limit condition even when the sensor reads correctly.

How To Diagnose A Goodman Furnace High Limit Switch Open

Safety First

Always turn off power to the furnace at the service switch or breaker before inspecting components. If gas work or combustion checks are needed, consider hiring a licensed HVAC technician to avoid safety risks.

Visual Inspection

Inspect filters, vents, and the furnace area for obvious airflow restrictions. Check the heat exchanger and burners for heavy soot or corrosion. Examine wiring to the limit switch for damage or loose connections.

Measure Airflow And Temperature

Check filters and replace if dirty. Confirm return and supply registers are open. Use a thermometer or infrared gun to compare furnace cabinet temperature with expected values; large hot spots near the heat exchanger suggest overheating.

Test The Blower Motor

Verify blower operation on heat and fan-only modes. Listen for unusual noises and check the blower capacitor for bulging or leaks. Reduced RPMs or failure to start indicates airflow issues that can trip the limit.

Use A Multimeter On The Limit Switch

With power off, remove the limit switch cover and test continuity across the limit terminals. A normally closed limit will show continuity at normal temperatures; an open reading indicates the switch is open or failed. Re-test after the system cools if it’s an automatic-reset type.

Check For Error Codes

Many Goodman furnaces have LED status codes on the control board. Refer to the unit’s manual to interpret flashes that may indicate limit trips, flame rollout, or blower faults.

Step-By-Step Troubleshooting And Repair

1. Replace Or Clean The Air Filter

Begin with the simplest action: replace disposable filters or clean reusable filters. Consistent filter maintenance often resolves overheating and keeps the limit switch from opening.

2. Inspect And Unblock Vents And Ducts

Open all registers, inspect attic/ crawlspace ducts for crushes or disconnections, and ensure exterior intake/ exhaust terminations are clear of debris. Proper airflow balance is essential to prevent limit trips.

3. Test And Service The Blower Assembly

Check blower belts (if applicable), motor bearings, and the capacitor. Replace a weak capacitor; lubricate or replace motors that show excessive wear. Restored blower operation frequently cures high-limit opens.

4. Clean Burners And Heat Exchanger

Remove burner assembly for cleaning if soot buildup is visible. Carefully clean the heat exchanger and check for cracks or heavy corrosion. Cracked heat exchangers present safety hazards and may require furnace replacement.

5. Check And Replace The High Limit Switch

If tests confirm the limit switch is open when the furnace is cool or shows no continuity, replace it with the Goodman OEM or equivalent rated switch. Ensure replacement part matches temperature rating and terminal configuration.

6. Repair Wiring And Control Board Issues

Tighten or replace corroded connectors. If the control board shows erratic behavior or incorrect responses to limit inputs, consult a trained technician for board diagnosis; replacement or reprogramming may be required.

7. Verify Proper Venting And Combustion

Ensure the flue and venting system are intact, pitched correctly, and free of obstructions. For power-vented or direct-vent models, confirm inducer motor and pressure switches operate correctly to avoid heat buildup.

When To Call A Professional HVAC Technician

DIY troubleshooting can address filters, vents, and basic testing, but professional service is recommended for gas valve work, heat exchanger inspection for cracks, control board replacement, or complex electrical diagnosis.

Call a licensed technician when there is evidence of flame rollout, cracked heat exchanger, gas leaks, or persistent limit trips that continue after basic maintenance. Certified techs have combustion analyzers, manometers, and replacement parts to repair safely.

Preventive Maintenance Tips To Avoid Future High Limit Opens

• Replace or clean the furnace air filter every 1–3 months depending on usage and filter type.
• Schedule annual professional tune-ups to inspect burners, heat exchanger, and blower.
• Keep supply and return registers unobstructed and maintain balanced ductwork.
• Monitor for unusual noises, odors, or frequent cycling and address them promptly.
• Install carbon monoxide detectors near sleeping areas and ensure proper venting.

Replacement Parts And Estimated Costs

A replacement Goodman high limit switch typically costs between $20 and $80 for the part. Professional service labor can add $100–$300 depending on travel and diagnostic time.

Blower motor or capacitor replacement ranges widely: capacitors $30–$100, motors $200–$600. Control board replacements can cost $200–$700 installed. Costs vary by model and region.

Key Diagnostic Checklist For Technicians And Homeowners

1. Confirm symptom: no heat, short cycling, or error codes.
2. Inspect and replace the air filter.
3. Verify blower operation and capacitor condition.
4. Test limit switch continuity with power off.
5. Check venting and combustion air paths for blockage.
6. Inspect heat exchanger and burners for buildup or damage.
7. Examine wiring and control board responses to limit inputs.

Useful Goodman Furnace Models And Limit Switch Notes

Goodman uses a variety of high limit switches across models; some are manual-reset while many are automatic. OEM part numbers differ by model series (GMVM, GMSS, GMUH, etc.). When replacing a limit, use model-specific cross-reference information or the furnace data plate to ensure compatibility.

Frequently Asked Questions

Can A High Limit Switch Be Reset?

Some high limit switches are automatic-reset types and will close again after cooling. Others are manual-reset and require pressing a reset button. If the switch trips repeatedly, the root cause must be addressed rather than relying on resets.

Is It Safe To Bypass The High Limit Switch?

Never bypass the high limit switch. It is a critical safety device designed to prevent overheating and potential fire hazards. Bypassing exposes property and occupants to serious risk and likely violates codes.

How Long Do High Limit Switches Last?

Lifespan varies with operating conditions; under normal use a limit switch can last many years, but frequent overheating cycles, moisture, or corrosion can shorten life. Regular maintenance extends component life.

Resources And Further Reading

Refer to the Goodman furnace installation and service manual for model-specific wiring diagrams and part numbers. For safety-critical repairs, consult an NATE-certified HVAC technician or the Goodman customer support portal.