High-efficiency gas furnaces, also known as condensing furnaces, are sophisticated heating systems that can save you hundreds of dollars a year with lower heating bills. Unfortunately, these advanced furnaces can suffer from many of the same malfunctions as conventional gas furnaces. A faulty flame sensor can cause any type of gas furnace to stop working.

What Are Furnace Flame Sensors?

High-efficiency gas furnaces do not rely on conventional pilot lights to provide ignition, as pilot lights waste a significant amount of gas. Instead, they use hot surface ignitors (HSIs) or electrical arc ignitors, which ignite the furnace's supply of propane or natural gas using electricity. 

If a high-efficiency furnace's arc ignitor or HSI stops functioning, the furnace may continue to pipe gas into the combustion chamber, creating the potential for a dangerous gas leak. Flame sensors are installed to prevent this from happening. If the sensor doesn't detect the heat created by gas ignition, it will automatically shut off the gas flow before a leak can occur.

What Happens When A Furnace Flame Sensor Malfunctions?

If your high-efficiency gas furnace's flame sensor malfunctions, it may not be able to detect the heat created by gas ignition, even if the furnace ignites correctly. The sensor will then automatically shut off the gas flow and deactivate the furnace after a few seconds, leaving your furnace useless. If your high-efficiency furnace has a digital readout, it may display an error code when this occurs.

What Should You Do If Your High-Efficiency Gas Furnace Has A Faulty Flame Sensor?

Because flame sensors are exposed to burning gas, they can become coated with soot and other solid combustion by-products over time. A thick layer of soot will prevent the sensor from functioning properly, but cleaning the sensor should restore its functionality.

You can attempt to clean a dirty flame sensor yourself, but only if you know exactly what you are doing. It is easy to accidentally damage other components while attempting to remove and clean a dirty flame sensor. You must also make sure not to touch the sensor with your bare hands—the natural oils on your skin can damage the porcelain rod at the end of the flame sensor, making a serious malfunction much more likely.

The safest approach is to have a professional heating system repair service inspect your furnace's flame sensor for you. These services can quickly and thoroughly clean the sensor without causing accidental damage, and inspect the sensor for malfunctions if cleaning the sensor does not solve the problem.

Professional repair services can also rule out other furnace problems that may be preventing the furnace from staying lit, such as dirty air filters or impinged air flow. 

For more information about heating system repair, contact a local company.