A functional furnace keeps your home warm and comfortable during cold weather. If your furnace suddenly stops working and disrupts your home’s comfort, understanding the causes of furnace failure can help you identify and address the problem quickly and potentially prevent further damage.
Top 7 Reasons Your Furnace May Stop Working
Furnaces are complex systems and can stop working for several reasons — some are minor, such as dirty air filters or dead thermostat batteries, while others may require more involved diagnosis and repair.
1. Thermostat issues
The thermostat is responsible for detecting and communicating temperature shifts to your furnace control board, which in turn coordinates each part of the heating cycle. Faulty thermostats can prevent your system from turning on when it should or may even keep your furnace running continuously.
Sometimes, the thermostat isn’t actually faulty and just needs the settings adjusted. If the thermostat is set to the wrong mode or at too low of a preset temperature, it won’t signal the furnace to turn on. Thermostat problems may also lie in their power sources. Wired-in thermostats may have damaged, loose, or faulty wiring that prevents it from receiving stable power. Other thermostats use batteries — if the batteries die, the thermostat won’t be responsive.
Thermostat components can also wear out or become miscalibrated, leading to faulty operation. For instance, dirty or damaged temperature sensors may cause inaccurate readings. Periodically check your thermostat settings, battery life, and calibration to ensure it’s operating correctly.
2. Tripped circuit breaker or blown fuse
Most modern furnaces have at least some electrical components, regardless of their fuel type. Mainly, many furnaces use an electric ignition system instead of pilot lights, therefore requiring a power supply to begin a heating cycle. Furnaces also use blower fans to circulate warm air, which operate on electricity.
An overworking blower is most commonly responsible for tripped circuit breakers or blown fuses. Dirty filters, closed or obstructed vents, damaged ductwork, and associated problems can restrict airflow, causing the blower and furnace to work harder to heat your home.
In other cases, tripped breakers or blown fuses may stem from inherent wiring problems, such as:
- Too many appliances on one circuit — furnaces typically need a dedicated circuit
- Damaged breakers
- Short circuits or ground circuits
- Insufficient circuit capacity
- Faulty electrical panel
- Insufficient electrical panel capacity
Reset a tripped circuit breaker by moving it to the off position, then back to the on position. Refer to your owner’s manual for instructions on replacing a blow fuse, or consult an electrician. If the breakers trip or fuses blow persistently, however, there’s likely a more significant underlying problem with your furnace or electrical system that requires a professional to inspect and repair.
3. Gas supply problems
If your gas furnace stops working, a disruption in the gas supply may be the culprit. Several parts manage gas supply and regulation during heating or standby cycles, and errors or faults with any of these can disrupt the flow. Consider these potential causes of gas supply issues:
- Closed gas valve: Gas valves control the flow of gas to the furnace. A partially or fully closed gas valve, whether due to damage, obstruction, or accidental closure, prevents gas from reaching the burner.
- Faulty gas pressure regulator: Pressure regulators maintain consistent pressure to prevent overheating and ensure safe combustion. A failing regulator may cause faulty ignition or unsafe conditions.
- Disconnected gas: Utility companies may temporarily shut off gas supply for maintenance or other circumstances. Check that the main gas valve is open, then contact your utility company if supply problems persist.
4. Malfunctioning pilot light
The pilot light is a continuous flame that ignites the gas burner during a heating cycle. If your pilot light is faulty, your furnace may shut down altogether — if it’s still running but the pilot light is unable to light the burner, it won’t produce heat. In some cases, pilot lights may struggle to stay lit because of gas supply problems, such as a closed valve. Since they affect the furnace’s precise ignition and combustion process, malfunctioning pilot lights pose several safety risks, including fire, explosion, and carbon monoxide or other exhaust fume leaks.
Several factors can cause a pilot light to malfunction, including:
- Faulty thermocouple: Thermocouples are safety devices made from copper rods. If they don’t detect the pilot light’s flame, they trigger a safety shutdown to prevent gas buildup. These devices may become misaligned, dirty, or worn, preventing them from properly detecting a light.
- Dirty pilot light: The pilot light assembly may become dirty or blocked, usually indicated by a partially yellow or flickering flame. This problem typically stems specifically from the pilot light orifice, which is located in the pilot light tube and controls the gas flow to the pilot light.
- Drafts: Excessive drafts around your furnace can blow out the pilot light, usually because of drafts from leaky ductwork or overly strong airflow from the return vent.
Avoid attempting to relight the pilot light without professional help if you’re unsure about the process.
5. Dirty or clogged air filter
A dirty air filter is one of the most common reasons for furnace failure, but it’s also easy to resolve. The filter traps dust, dirt, and other debris as it enters the heating system, helping to maintain the cleanliness of your indoor air and internal furnace components. For optimal function, air filters require replacement every one to three months.
If the filter becomes clogged, it’s less effective at filtering these particles and may cause dirt and debris to accumulate on furnace parts and accelerate wear. A clogged filter also restricts airflow, which causes the furnace to work harder and potentially overheat, in which case the safety sensors trigger a shutdown.
6. Blower motor failure
The blower motor and fan circulate heated air throughout your home. A malfunctioned blower motor prevents heat distribution, potentially causing hot or cold spots throughout your home or preventing heating altogether.
Blower motors fail for several reasons, such as:
- Overheating from restricted airflow.
- Damaged electrical components.
- Loose fasteners and other parts.
- Bent fan blades.
- Dust and dirt buildup.
- Insufficient lubrication.
7. Blocked or closed vents
Vents should generally be left open and unobstructed to maintain consistent ductwork airflow and pressure. Imbalanced pressure restricts airflow, disrupting the combustion process and potentially causing the furnace to overheat. Restricted airflow likewise overworks other parts of your heating system, including ductwork and the blower motor, preventing it from efficiently heating your home.
Call Frank’s for Furnace Repair
If your gas or electric furnace has stopped working as it should, Frank’s Repair Plumbing is ready to help residents in Amarillo, Canyon, and other Texas Panhandle areas. Contact us or schedule online for any furnace need, from routine tune-ups to emergency repairs.
Frequently Asked Questions
Can I fix a furnace myself?
Resetting the thermostat, changing an air filter, and similarly minor tasks are reasonable DIY repairs for homeowners. More complex problems should be left to professionals to prevent further damage or safety hazards.
How can I prevent future furnace breakdowns?
Routine maintenance and inspections are the best way to prevent breakdowns. These services identify and resolve minor issues that come with age and usage, prolonging your furnace’s service life and optimizing its efficiency and reliability.
