When your furnace is blowing air but the air is cold, it usually means the blower fan is working but the heating element or gas burners have failed to ignite.
A furnace running with no heat (fan only) is usually caused by a dirty air filter, ignition failure, or a tripped safety switch (limit switch). The fan continues to run to cool down the system, while the burners fail to ignite or shut down. Key checks include replacing the filter and ensuring the gas valve is open.
Resetting a gas furnace is generally a straightforward process that works much like rebooting a computer. The most common method is using the main power switch or circuit breaker.
Running your furnace fan constantly can improve indoor air quality and balance temperatures, but it does increase energy usage. For most households, it is best to use the "Auto" setting during summer to prevent humidity issues, and switch to "ON" or "Circulate" during winter to keep air fresh and rooms evenly heated.
If your furnace is blowing cold air, it usually indicates the blower motor is working but the burners are not generating heat. A dirty flame sensor may fail to confirm a flame, shutting down the burners for safety. Ignition problems, such as a worn ignitor or gas supply issue, can also stop proper heating.
Reset the Furnace
Turn the thermostat to "OFF." Locate the power switch on the furnace (often looks like a light switch) or the circuit breaker. Turn it off for 30 seconds, then flip it back on. Turn the thermostat back to "HEAT."
5 Warning Signs It's Time for Furnace Replacement
If you use your fan purely for air circulation or filtration, 15 to 20 minutes per hour is the industry-recommended sweet spot. This keeps the air fresh, helps balance temperatures across rooms, and filters out allergens without causing excessive wear and tear on your blower motor.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.
The $5,000 rule is a guideline to help homeowners decide whether to repair or replace their HVAC system. You multiply the age of your unit by the cost of the needed repair. If that number exceeds $5,000, replacing your HVAC system is often more cost-effective.
Your furnace’s reset button is typically a small, bright red or yellow button located either inside the blower compartment, near the burner assembly, or directly on the motor housing.
The Most Common Home Heating Problems
To reset your furnace, turn off the power at the main breaker or emergency switch and wait 30 seconds to 5 minutes before turning it back on. This brief wait allows the electrical components to fully power down and ensures the system's computer reboots properly.
When your furnace won't kick on, start by checking the thermostat (ensure it’s set to "heat" and the temperature is turned up) and replace the air filter if it’s dirty. Next, verify the system's power by resetting the dedicated circuit breaker and checking the emergency switch on or near the unit.
A frozen pipes furnace failure can cause major problems inside your home. Ice builds up fast in unheated spaces, and when frozen water expands, it can burst pipes wide open. That kind of mess is the last thing anyone wants during a winter heating outage.
A bad or clogged heater core is usually indicated by little to no heat from the vents, a sweet, syrupy smell inside the cabin, foggy windows, or damp, sticky carpets.
What fails first on a furnace? The most common early failures are the furnace ignitor or flame sensor, as they experience regular wear and tear and are critical to starting the heating cycle.
A furnace typically lasts between 15 and 20 years. However, the exact lifespan varies based on the type of unit and how well it is maintained.
Homeowners insurance may cover the cost to repair or replace your furnace or boiler if it's damaged or destroyed by a covered peril. Covered perils as defined by your policy typically include events such as: Lightning. Fire.
A typical furnace runs for approximately 10 to 15 minutes per cycle, cycling three to eight times per hour. A short cycling system runs for less than five minutes, then quickly restarts, often cycling much more frequently. This pattern prevents efficient heating and creates massive strain on your equipment.
Although comfort is personal and can vary, a generally comfortable temperature for a house is often set between 68 and 72 degrees Fahrenheit. This range is considered ideal for most people to feel comfortable indoors.
Running your furnace fan constantly can improve indoor air quality and balance temperatures, but it does increase energy usage. For most households, it is best to use the "Auto" setting during summer to prevent humidity issues, and switch to "ON" or "Circulate" during winter to keep air fresh and rooms evenly heated.
Short cycling
This is one of the most common furnace problems, and it can stress important furnace components such as the blower motor, limit switch, or flame sensor. There are several potential causes of short cycling, including some that are related to your furnace's built-in safety systems.
You should probably Replace if: [ ] The repair costs more than 50% of a new unit. [ ] The furnace is over 15 years old. [ ] You have had to repair it more than once in the last 2 years.
Subtle Signs Your Furnace Is Starting to Break Down
Here's what to watch for: Increased Utility Bill: A sudden spike in your utility bill can signal inefficiency in your furnace, often a sign it's working harder than usual. Strange Noises: Unusual sounds, like banging or whistling, might indicate internal issues.