A furnace will light, but it will only stay lit for about 3 to 10 seconds before shutting off. The flame sensor acts as a safety device; if it doesn't detect a flame, it triggers the system to shut off the gas valve to prevent unburned gas from accumulating in your home.
When the sensor malfunctions, the furnace may shut down, fail to ignite, or blow cold air, leading to discomfort and higher energy costs. Identifying these issues early helps prevent unexpected breakdowns and costly furnace repairs.
If your furnace shuts off after just a few seconds of running, this could point to a flame sensor issue. This happens because the flame sensor is not detecting the flame properly, so the system shuts down as a safety precaution.
To get your furnace to kick on, first verify your thermostat is set to "Heat" and raised at least 5 degrees above room temperature. Next, check that the furnace power switch (usually resembling a standard light switch on or near the unit) is toggled "ON".
When your furnace clicks but refuses to turn on, it typically means the electronic ignition sequence has failed. This is often caused by a dirty flame sensor, a cracked or burnt-out igniter, or a faulty gas valve.
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.
You cannot safely bypass a furnace flame sensor. It is a critical safety device that proves a flame is present. If you bypass it, the gas valve will remain open when there is no fire, filling your home with gas and creating a major explosion and fire hazard.
5 Warning Signs It's Time for Furnace Replacement
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.
6 Reasons Why Your Furnace is Not Igniting
Furnaces should cycle 3-8 times per hour. Short cycles may indicate oversized units or airflow issues. Long cycles can signal undersized furnaces or insulation problems. Regular maintenance helps ensure proper cycling and performance.
Capacitors are used in nearly every heating system, from gas furnaces to electric furnaces to heat pumps. Even though other parts can fail, like the ignitor in a gas furnace or the compressor in a heat pump, the capacitor is by far the most common part to fail on a furnace because almost every system relies on one.
Visual Inspection
Start by turning off your furnace power to stay safe. Look carefully at the flame sensor's metal rod. Check if it's dirty, rusty, or coated with soot. Dirt or buildup can stop it from sensing the flame properly.
Dust, other contaminants, vibrations, shocks and exposure to high temperatures all have a shortening effect on the average lifespan of a sensor, so it is important to look for a solution that overcomes these problems by design, rather than just accepting frequent sensor failure and replacement as part and parcel of ...
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.
A standard residential furnace lasts 15 to 20 years. However, the exact lifespan varies based on the type of system and how well it is maintained.
You know it is time to replace your furnace when it is over 15 to 20 years old, requires increasingly expensive repairs, or struggles to maintain consistent heating. Waiting for a total, freezing-weather breakdown leaves you with higher costs and limited options, so being proactive is crucial.
If your furnace lights up, runs for a few seconds, and then shuts off (a process called "short cycling"), your flame sensor is usually the culprit. The sensor verifies the fire is lit; when it fails to do so, it shuts off the gas supply as a safety measure.
Furnace Flame Sensor Replacement Costs
Professional replacement generally falls in the $75 to $250 range, which includes the part and labor. The wide range depends on your location, the technician's service call fee, and whether the visit is during regular hours or an emergency call.
A furnace flame sensor should generally be cleaned once a year, usually at the start of the heating season. However, homes with pets, heavy dust, or appliances that produce airborne debris (like laundry lint) may require cleaning more than once a season.
If it doesn't start at all, you can press the button one more time. But, if you press the reset button and your furnace goes on and turns off again, don't press the button again. Continuing to press the reset button can damage your system. Doing so will pump more oil into the furnace and worsen any existing issues.
To reset a furnace, lower your thermostat to the lowest setting. Turn off power using the furnace's emergency switch or circuit breaker. Wait 2-5 minutes, turn the power back on, and adjust your thermostat. If the furnace locked out due to a safety issue, you may need to press the reset button.
As the filter becomes more clogged, it can cause other parts of the furnace, such as the blower motor or heat exchanger, to overwork and eventually fail. Replacing these components can be costly, and in severe cases, you might even need to replace the entire furnace.