In-stock parts ship the same dayFurnace Repair FAQs: Troubleshooting, Parts & Fixes
Start by matching the symptom to the problem: not heating, noisy operation, starts then stops, blower not running, blower runs all the time, weak airflow, not turning on, burners will not stay lit, long heat times, strange smells, short cycling, poor temperature control, breaker trips, or wall thermostat problems. Check simple causes first, including the thermostat setting, air filter, breaker, furnace switch, access panel, and visible fault code. Use the furnace repair help page to choose the closest troubleshooting path.
Use the model number from your furnace label to filter parts that fit your exact unit. Furnace parts can vary by brand, fuel type, voltage, size, and control setup, so do not rely on appearance alone. Start with furnace replacement parts to narrow by model, symptom, or part category.
A furnace that is not heating may have a failed igniter, dirty flame sensor, pressure switch problem, faulty gas valve, bad control board, limit switch issue, clogged filter, thermostat problem, or ignition control failure. Check the air filter, thermostat, furnace switch, breaker, and any diagnostic fault code before replacing parts. Use furnace not heating troubleshooting to compare the most common causes.
Yes. A Hot Surface Igniter or Spark Igniter starts the burner sequence. If the igniter fails, the burners may not light and the furnace may lock out after the failed ignition attempt. Inspect for cracks or visible damage, then test the igniter according to the service information for your model. Match the correct replacement through furnace igniter parts.
Yes. The flame sensor confirms that the burners have lit. If the sensor is dirty or weak, the furnace may light briefly and then shut down because the control board does not detect flame. Clean the sensor if the model allows it, then replace it if the problem continues and testing points to the sensor. Find a match through furnace flame sensor parts.
A noisy furnace may have a loose blower wheel, worn blower motor bearings, loose panel, dirty burner, failing inducer motor, rattling duct, or vibration issue. Listen for when the noise happens, such as during startup, burner ignition, blower operation, or shutdown. Use furnace noisy or loud troubleshooting to narrow the source.
Yes. A loose, dirty, or damaged blower wheel can wobble on the motor shaft and create rattling, scraping, or vibration. Turn off power before inspecting the blower compartment, then check whether the wheel is rubbing the housing or loose on the shaft. If it is cracked or damaged, compare furnace blower wheel and fan blade parts.
A furnace that starts and then stops may have a dirty flame sensor, pressure switch issue, restricted vent, clogged condensate trap, faulty igniter, limit switch problem, or control board fault. The furnace may shut down as a safety response when it cannot prove flame or airflow. Use furnace starts then stops troubleshooting to follow the diagnostic sequence.
Yes. The pressure switch confirms that the draft inducer has established proper venting before the furnace lights. A clogged condensate trap, blocked vent, restricted heat exchanger, weak inducer motor, or failed pressure switch can interrupt the heating cycle. If testing points to the switch, compare furnace pressure switch parts.
If the furnace blower is not running, check the blower motor, capacitor, control board, relay, limit switch, door switch, thermostat signal, and incoming power. A failed capacitor can keep some blower motors from starting, while a failed board or relay may keep power from reaching the motor. Use furnace blower not running troubleshooting before replacing the motor.
Yes. A failing blower motor may hum, run slowly, overheat, stop intermittently, or fail to start even when power is present. Check for a seized blower wheel, bad capacitor, and proper voltage before replacing the motor. Match the correct replacement through furnace motor parts.
A blower that runs all the time may be caused by the thermostat fan setting, stuck relay, bad control board, failed fan limit switch, shorted thermostat wiring, or a limit switch keeping the blower on for safety. Make sure the thermostat fan setting is on Auto before replacing parts. Use furnace blower runs all the time troubleshooting to narrow the cause.
Yes. A fan limit switch can keep the blower running if it is stuck, misreading temperature, or responding to an overheating condition. Check the air filter and airflow first because poor airflow can trigger limit-related operation. If testing points to a failed switch, compare furnace switch parts.
Weak furnace airflow can be caused by a dirty air filter, blocked registers, dirty blower wheel, weak blower motor, duct restriction, closed dampers, or incorrect blower speed. Start with the filter and registers before opening the blower compartment. Use furnace not blowing enough troubleshooting to check the airflow path.
Yes. A clogged furnace filter restricts return airflow, reduces heat delivery, and can make the furnace overheat or cycle on the limit switch. Replace the filter with the correct size and airflow rating for the system. If airflow remains weak, check the blower wheel, blower motor, ducts, and registers.
A furnace that will not turn on may have a thermostat problem, tripped breaker, blown fuse, failed transformer, open door switch, bad control board, faulty igniter, or incoming power issue. Confirm the thermostat is calling for heat, the furnace switch is on, and the access panel is seated. Use furnace not turning on troubleshooting to follow the repair path.
Yes. The transformer supplies low voltage to the thermostat and control circuit. If it fails, the thermostat may be blank, the furnace may not respond, or the control board may not receive the signal it needs. If the transformer is damaged or tests bad, match a replacement through furnace transformer parts.
Burners that light and then go out may be caused by a dirty flame sensor, gas valve issue, pressure switch problem, ignition control failure, restricted vent, or control board fault. The furnace shuts the burners off when it cannot confirm safe operation. Use furnace burners will not stay lit troubleshooting to compare the likely causes.
Yes. The gas valve controls gas flow to the burners, and a failed valve can prevent ignition or cause burner operation to stop. Confirm the igniter, flame sensor, pressure switch, and gas supply before replacing the valve. If testing points to the valve, compare furnace gas burner and control valve parts. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely.
A furnace that takes too long to heat may have a clogged air filter, weak blower, dirty blower wheel, poor duct airflow, thermostat issue, undersized system, burner problem, or heat exchanger airflow restriction. Start with airflow because poor airflow slows heat delivery and can create overheating problems. Use furnace takes too long to heat troubleshooting to narrow the issue.
If the blower runs constantly but there is no heat, the furnace may have an ignition problem, dirty flame sensor, failed igniter, pressure switch issue, open limit switch, gas valve problem, or control board fault. The blower can continue running while the burner section is locked out or prevented from firing. Use furnace blower running with no heat troubleshooting to check the heating sequence.
Strange furnace smells can come from dust burning off at startup, clogged filters, overheating components, electrical problems, gas issues, or foreign objects near the heat exchanger or blower. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely. Shut the furnace off if you smell electrical burning or see smoke. Use strange furnace smell troubleshooting to separate normal startup odors from safety concerns.
Short cycling can be caused by a dirty air filter, blocked vents, overheating, thermostat placement, bad flame sensor, pressure switch issue, oversized furnace, control board fault, or limit switch problem. Check airflow first because restricted airflow is a common cause of overheating and rapid cycling. Use furnace short cycling troubleshooting to compare likely causes.
Poor temperature control may be caused by a thermostat issue, poor thermostat location, dirty filter, weak blower, duct restriction, control board problem, or system sizing issue. Make sure the thermostat is not near drafts, supply vents, direct sunlight, or heat sources. Use furnace poor temperature control troubleshooting before replacing parts.
Yes. A bad wall thermostat, WiFi thermostat, thermostat wiring problem, or dead thermostat battery can prevent the furnace from turning on, cause short cycling, keep the blower running, or create poor temperature control. Check the settings, batteries, wiring, and heat call before replacing furnace parts. Match compatible replacements through furnace thermostat parts.
A tripping breaker can be caused by a shorted blower motor, shorted inducer motor, damaged wire harness, shorted control board, failed transformer, or a household electrical issue. If the breaker trips repeatedly, stop resetting it until the short is found. Use furnace breaker troubleshooting and have unsafe electrical issues handled by a qualified technician.
Yes, but control boards are often misdiagnosed, so check power, thermostat signal, igniter, flame sensor, pressure switch, limit switch, blower motor, and wiring first. A failed board may prevent the furnace from starting, heating, running the blower correctly, or reading safety inputs. If testing points to the board, compare furnace circuit board and timer parts.
A wall thermostat problem may involve dead batteries, incorrect settings, loose thermostat wiring, a failed thermostat, bad transformer, poor thermostat location, or control board issue. If the display is blank, check batteries and low-voltage power first. Use furnace wall thermostat troubleshooting to work through common causes.
Use a licensed HVAC technician for gas leaks, cracked heat exchangers, combustion problems, venting problems, gas valve replacement when required by code, repeated breaker trips, and any repair involving unsafe wiring or combustion testing. DIYers can often handle filters, thermostat batteries, some igniters, flame sensors, switches, and model-specific parts when proper safety steps are followed. Stop if you smell gas, see flame rollout, find damaged wiring, or are unsure about the repair. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely.
Your furnace model number is usually listed on a rating label inside the furnace cabinet, behind the access panel, near the burner assembly, or on the side panel. Use the full model number, not just the brand or serial number, so you can match parts correctly. If you need help locating it, use the furnace model number help page before shopping for parts.
Start by matching the symptom to the problem: not heating, noisy operation, starts then stops, blower not running, blower runs all the time, weak airflow, not turning on, burners will not stay lit, long heat times, strange smells, short cycling, poor temperature control, breaker trips, or wall thermostat problems. Check simple causes first, including the thermostat setting, air filter, breaker, furnace switch, access panel, and visible fault code. Use the furnace repair help page to choose the closest troubleshooting path.
Use the model number from your furnace label to filter parts that fit your exact unit. Furnace parts can vary by brand, fuel type, voltage, size, and control setup, so do not rely on appearance alone. Start with furnace replacement parts to narrow by model, symptom, or part category.
A furnace that is not heating may have a failed igniter, dirty flame sensor, pressure switch problem, faulty gas valve, bad control board, limit switch issue, clogged filter, thermostat problem, or ignition control failure. Check the air filter, thermostat, furnace switch, breaker, and any diagnostic fault code before replacing parts. Use furnace not heating troubleshooting to compare the most common causes.
Yes. A Hot Surface Igniter or Spark Igniter starts the burner sequence. If the igniter fails, the burners may not light and the furnace may lock out after the failed ignition attempt. Inspect for cracks or visible damage, then test the igniter according to the service information for your model. Match the correct replacement through furnace igniter parts.
Yes. The flame sensor confirms that the burners have lit. If the sensor is dirty or weak, the furnace may light briefly and then shut down because the control board does not detect flame. Clean the sensor if the model allows it, then replace it if the problem continues and testing points to the sensor. Find a match through furnace flame sensor parts.
A noisy furnace may have a loose blower wheel, worn blower motor bearings, loose panel, dirty burner, failing inducer motor, rattling duct, or vibration issue. Listen for when the noise happens, such as during startup, burner ignition, blower operation, or shutdown. Use furnace noisy or loud troubleshooting to narrow the source.
Yes. A loose, dirty, or damaged blower wheel can wobble on the motor shaft and create rattling, scraping, or vibration. Turn off power before inspecting the blower compartment, then check whether the wheel is rubbing the housing or loose on the shaft. If it is cracked or damaged, compare furnace blower wheel and fan blade parts.
A furnace that starts and then stops may have a dirty flame sensor, pressure switch issue, restricted vent, clogged condensate trap, faulty igniter, limit switch problem, or control board fault. The furnace may shut down as a safety response when it cannot prove flame or airflow. Use furnace starts then stops troubleshooting to follow the diagnostic sequence.
Yes. The pressure switch confirms that the draft inducer has established proper venting before the furnace lights. A clogged condensate trap, blocked vent, restricted heat exchanger, weak inducer motor, or failed pressure switch can interrupt the heating cycle. If testing points to the switch, compare furnace pressure switch parts.
If the furnace blower is not running, check the blower motor, capacitor, control board, relay, limit switch, door switch, thermostat signal, and incoming power. A failed capacitor can keep some blower motors from starting, while a failed board or relay may keep power from reaching the motor. Use furnace blower not running troubleshooting before replacing the motor.
Yes. A failing blower motor may hum, run slowly, overheat, stop intermittently, or fail to start even when power is present. Check for a seized blower wheel, bad capacitor, and proper voltage before replacing the motor. Match the correct replacement through furnace motor parts.
A blower that runs all the time may be caused by the thermostat fan setting, stuck relay, bad control board, failed fan limit switch, shorted thermostat wiring, or a limit switch keeping the blower on for safety. Make sure the thermostat fan setting is on Auto before replacing parts. Use furnace blower runs all the time troubleshooting to narrow the cause.
Yes. A fan limit switch can keep the blower running if it is stuck, misreading temperature, or responding to an overheating condition. Check the air filter and airflow first because poor airflow can trigger limit-related operation. If testing points to a failed switch, compare furnace switch parts.
Weak furnace airflow can be caused by a dirty air filter, blocked registers, dirty blower wheel, weak blower motor, duct restriction, closed dampers, or incorrect blower speed. Start with the filter and registers before opening the blower compartment. Use furnace not blowing enough troubleshooting to check the airflow path.
Yes. A clogged furnace filter restricts return airflow, reduces heat delivery, and can make the furnace overheat or cycle on the limit switch. Replace the filter with the correct size and airflow rating for the system. If airflow remains weak, check the blower wheel, blower motor, ducts, and registers.
A furnace that will not turn on may have a thermostat problem, tripped breaker, blown fuse, failed transformer, open door switch, bad control board, faulty igniter, or incoming power issue. Confirm the thermostat is calling for heat, the furnace switch is on, and the access panel is seated. Use furnace not turning on troubleshooting to follow the repair path.
Yes. The transformer supplies low voltage to the thermostat and control circuit. If it fails, the thermostat may be blank, the furnace may not respond, or the control board may not receive the signal it needs. If the transformer is damaged or tests bad, match a replacement through furnace transformer parts.
Burners that light and then go out may be caused by a dirty flame sensor, gas valve issue, pressure switch problem, ignition control failure, restricted vent, or control board fault. The furnace shuts the burners off when it cannot confirm safe operation. Use furnace burners will not stay lit troubleshooting to compare the likely causes.
Yes. The gas valve controls gas flow to the burners, and a failed valve can prevent ignition or cause burner operation to stop. Confirm the igniter, flame sensor, pressure switch, and gas supply before replacing the valve. If testing points to the valve, compare furnace gas burner and control valve parts. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely.
A furnace that takes too long to heat may have a clogged air filter, weak blower, dirty blower wheel, poor duct airflow, thermostat issue, undersized system, burner problem, or heat exchanger airflow restriction. Start with airflow because poor airflow slows heat delivery and can create overheating problems. Use furnace takes too long to heat troubleshooting to narrow the issue.
If the blower runs constantly but there is no heat, the furnace may have an ignition problem, dirty flame sensor, failed igniter, pressure switch issue, open limit switch, gas valve problem, or control board fault. The blower can continue running while the burner section is locked out or prevented from firing. Use furnace blower running with no heat troubleshooting to check the heating sequence.
Strange furnace smells can come from dust burning off at startup, clogged filters, overheating components, electrical problems, gas issues, or foreign objects near the heat exchanger or blower. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely. Shut the furnace off if you smell electrical burning or see smoke. Use strange furnace smell troubleshooting to separate normal startup odors from safety concerns.
Short cycling can be caused by a dirty air filter, blocked vents, overheating, thermostat placement, bad flame sensor, pressure switch issue, oversized furnace, control board fault, or limit switch problem. Check airflow first because restricted airflow is a common cause of overheating and rapid cycling. Use furnace short cycling troubleshooting to compare likely causes.
Poor temperature control may be caused by a thermostat issue, poor thermostat location, dirty filter, weak blower, duct restriction, control board problem, or system sizing issue. Make sure the thermostat is not near drafts, supply vents, direct sunlight, or heat sources. Use furnace poor temperature control troubleshooting before replacing parts.
Yes. A bad wall thermostat, WiFi thermostat, thermostat wiring problem, or dead thermostat battery can prevent the furnace from turning on, cause short cycling, keep the blower running, or create poor temperature control. Check the settings, batteries, wiring, and heat call before replacing furnace parts. Match compatible replacements through furnace thermostat parts.
A tripping breaker can be caused by a shorted blower motor, shorted inducer motor, damaged wire harness, shorted control board, failed transformer, or a household electrical issue. If the breaker trips repeatedly, stop resetting it until the short is found. Use furnace breaker troubleshooting and have unsafe electrical issues handled by a qualified technician.
Yes, but control boards are often misdiagnosed, so check power, thermostat signal, igniter, flame sensor, pressure switch, limit switch, blower motor, and wiring first. A failed board may prevent the furnace from starting, heating, running the blower correctly, or reading safety inputs. If testing points to the board, compare furnace circuit board and timer parts.
A wall thermostat problem may involve dead batteries, incorrect settings, loose thermostat wiring, a failed thermostat, bad transformer, poor thermostat location, or control board issue. If the display is blank, check batteries and low-voltage power first. Use furnace wall thermostat troubleshooting to work through common causes.
Use a licensed HVAC technician for gas leaks, cracked heat exchangers, combustion problems, venting problems, gas valve replacement when required by code, repeated breaker trips, and any repair involving unsafe wiring or combustion testing. DIYers can often handle filters, thermostat batteries, some igniters, flame sensors, switches, and model-specific parts when proper safety steps are followed. Stop if you smell gas, see flame rollout, find damaged wiring, or are unsure about the repair. If you smell gas, shut off the gas supply at the appliance valve, ventilate the area, avoid sparks or flames, and contact your gas utility. Do not attempt gas-line repairs without the training and tools to do them safely.