Goodman Furnace Fan Won’t Turn Off: Causes, Fixes, and Costs

The Goodman furnace fan running continuously is a common issue that can increase energy bills and cause wear. This article explains likely causes, step-by-step troubleshooting, safe fixes, parts to check, estimated repair costs, and when to contact a professional technician. It helps homeowners resolve or diagnose a Goodman furnace fan that won’t turn off.

Symptom	Common Causes	Likely Fix
Fan runs constantly	Thermostat Fan Set To On, Blower Limit Switch, Stuck Relay, Faulty Control Board, Shorted Wiring	Change thermostat to Auto, replace switch/relay, repair wiring, replace control board
Fan runs after shutdown	Delayed Cooldown Feature, Faulty Delay Timer, Motor Overheating	Test delay relay, replace timer, inspect motor

How Goodman Furnace Fans Normally Operate

Understanding normal operation clarifies when the blower should run. The furnace blower runs during heating cycles and may run briefly after burner shutdown for heat distribution. The thermostat typically controls the fan using the G (fan) wire or internal settings (On vs Auto). Control boards and relays manage power to the blower motor. When components work correctly, the fan cycles only as needed.

Common Reasons The Goodman Furnace Fan Won’t Turn Off

Thermostat Set To Fan “On”

Many times the simplest cause is the thermostat fan setting. If the thermostat fan is set to On instead of Auto, the blower will run continuously regardless of heating cycles.

Stuck Or Faulty Fan Limit Switch

Older Goodman furnaces may use a mechanical fan limit switch to switch the blower on and off based on heat. A stuck or failed limit switch can keep the fan energized even when not needed.

Relay Or Contactor Stuck Closed

A stuck blower relay or contactor on the furnace control board can keep power applied to the blower motor. Mechanical relays can weld contacts, and solid-state relays can fail closed.

Faulty Furnace Control Board

The furnace control board coordinates signals from the thermostat to the blower. A malfunctioning control board can send continuous G signals or provide constant power to the fan circuit.

Shorted Wiring Or Miswired Thermostat

Wiring issues between the thermostat and furnace can create a continuous call for the fan. A short between the G wire and R (24V hot) or miswired connections can energize the fan relay.

Blower Motor Run Capacitor Or Motor Problems

If the blower motor is overheating or has a failed start/run capacitor, it can behave irregularly. Some motors have built-in thermal switches that latch or fail and keep the motor running or cycling oddly.

Thermostat Software Or Programming Issues

Modern smart thermostats may have fan schedules, “circulation” settings, or firmware bugs that cause continuous fan operation. Incorrect programming or a software glitch can be the culprit.

Safety First: Precautions Before Troubleshooting

Always shut power to the furnace at the breaker before opening the furnace access panel. Turn off the thermostat to avoid accidental calls. Use a voltage tester when working with wiring. If uncomfortable with electrical or gas components, call a licensed HVAC technician.

Step-By-Step Troubleshooting Guide

1. Check Thermostat Fan Setting

Set the thermostat fan to Auto and observe whether the blower stops. If it stops, the issue is the thermostat setting, not the furnace.

2. Inspect Thermostat Wiring And Reset

Turn off power, remove the thermostat cover, and ensure the G wire is connected correctly and not touching other terminals. Re-seat wires and perform a thermostat reset or replace batteries. Test after restoring power.

3. Test For A Constant G Signal

With the thermostat off, measure 24VAC between the G and C (or G and B depending on system) terminals at the furnace or thermostat. Continuous 24VAC indicates a stuck relay on the control board or a shorted thermostat.

4. Bypass The Thermostat Safely

Temporarily disconnect the G wire at the furnace and insulate it. If the fan stops, the issue is upstream (thermostat or wiring). If it continues, the problem is inside the furnace (relay, control board, or motor).

5. Inspect The Fan Relay And Control Board

Visually inspect the control board for burnt components, melted connectors, or a stuck relay. Some Goodman units have a separate blower relay that can be tested or swapped if spare relays are available.

6. Test The Blower Motor And Capacitor

Listen for humming, inspect the motor for heat, and test the capacitor with a multimeter that has capacitance measurement. A failing capacitor can cause irregular blower behavior, though it more commonly prevents starting.

7. Check Mechanical Fan Limit Switches

If present, test or replace the fan limit switch. Use a multimeter to verify the switch transitions open/closed at temperature or manually operate the lever to test if the blower responds correctly.

DIY Fixes Homeowners Can Try

Reset Or Replace Thermostat

Reset the thermostat to factory settings or replace an older thermostat. Many continuous fan issues are resolved by setting the thermostat correctly or replacing a faulty unit.

Clean And Tighten Wiring Connections

Loose or corroded wiring can create shorts. Tighten terminal screws, replace damaged wires, and clean contacts to reduce miscommunication between thermostat and furnace.

Replace A Faulty Fan Limit Switch Or Relay

If testing shows a failed limit switch or relay, these parts are relatively inexpensive and can be replaced by someone comfortable working inside the furnace after cutting power. Always follow the furnace manual for part numbers and procedures.

Replace Control Board Only If Necessary

Control board replacement is more complex and costly. Replace the control board only after confirming the board is at fault using diagnostic LEDs, error codes, or professional testing.

When To Call A Professional HVAC Technician

Contact a licensed HVAC technician if the problem involves gas components, if the control board or wiring diagnosis is unclear, or if the homeowner is uncomfortable with electrical repairs. A professional can read control board diagnostics, safely replace parts, and verify correct airflow and thermostat communication.

Parts, Labor, And Typical Repair Costs

Repair costs vary by region, unit age, and the specific part. Replace a thermostat: $75–$300 including basic installation. Relay or fan limit switch replacement: $100–$300. Blower motor capacitor: $50–$150. Blower motor replacement: $300–$900. Control board replacement: $250–$700. Labor and emergency call fees can add $100–$200.

Preventive Maintenance To Avoid Fan Issues

Regular HVAC maintenance reduces failures. Replace air filters every 1–3 months, keep vents and returns unobstructed, schedule annual tune-ups, and have a technician clean and lubricate the blower assembly. Inspect thermostat batteries and wiring annually.

How To Tell If The Fan Is Running For A Valid Reason

Determine if the fan runs only when heating is active or during cooling cycles. A short post-heat run for heat distribution is normal. Continuous running with the thermostat set to Auto is not normal and indicates an issue. Use the furnace’s diagnostic LED codes to confirm system status.

Advanced Diagnostics For Technicians

Technicians will check 24VAC signals at the thermostat and furnace, verify relay coil voltages, test motor amperage against nameplate, examine control board solder joints and connectors, and use an HVAC multimeter and meter clamp to identify intermittent faults. They may also update thermostat firmware or replace noisy limit switches.

Common Misconceptions

Some homeowners assume the fan should always run for better air quality; however, continuous fan operation increases energy usage and may be unnecessary. Others believe replacing the thermostat always solves the problem; while often true, internal furnace component failures also cause persistent fan operation.

Useful Troubleshooting Checklist

• Thermostat Fan Setting: Set to Auto.
• Thermostat Wiring: Inspect G, R, C wires for shorts or loose connections.
• Control Board Lights: Note any error codes.
• Bypass Test: Disconnect G at furnace to isolate cause.
• Relay/Limit Switch: Inspect and test for continuity.
• Blower Motor: Check sound, heat, and capacitor.

Replacement Parts And Where To Buy

Buy OEM Goodman parts from authorized dealers or reputable HVAC suppliers. Generic parts are available but ensure compatibility by matching model and part numbers from the furnace’s data plate. For thermostats, choose models compatible with the system type (single-stage, multistage, heat pump).

When Continuous Fan Operation Is Acceptable

Continuous fan use may be chosen intentionally to improve filtration and air circulation. Modern thermostats often have an “on” setting for this purpose. If used intentionally, ensure the homeowner understands the increased energy cost and potential blower wear.

Key Takeaways For Homeowners

Start with the thermostat: set the fan to Auto and inspect wiring. Use basic tests (measure 24VAC, bypass G) to determine if the issue is a thermostat or internal furnace component. Replace inexpensive parts like relays, limit switches, and capacitors when clearly faulty. Call a licensed HVAC technician for control board, motor replacement, or any gas-related concerns.

For persistent problems, document the steps taken and any error codes to share with the technician; this speeds up diagnosis and may reduce repair costs. Addressing continuous fan operation promptly saves energy and prevents further system wear.