If your furnace kicks on and then shuts down right away, the cause might be the flame sensor in the combustion area of your gas furnace. The sensor has to detect flames, or the furnace shuts down.

After a few cycles of this, the furnace may shut down for an extended time to let you know something is wrong. Here's a look at what causes this problem in your furnace and what a heating repair professional can do to make the sensor work as it should.

Why The Sensor Keeps Your Furnace From Working

Under normal conditions, when your furnace starts, the gas turns on and ignites the burners. The sensor then detects the flames due to the increase in temperature and sends a signal to the control board that the furnace is starting up properly.

When the sensor is unable to detect the flame, even if the burners are working properly, the unit shuts down so gas doesn't build up. The sensor can shut down the furnace as a safety measure if the burners don't turn on, and it can also shut down the furnace if the burners turn on but the sensor doesn't detect the heat.

Why The Flame Sensor Malfunctions

A common cause of problems with the flame sensor is when it gets coated in carbon and soot. The sensor is a small metal probe that is near the flames, so it is exposed to the combustion process. Over time, the sensor can get coated with soot, dust, and carbon. When that happens, the probe can't detect temperature changes and the sensor won't work.

Another problem that develops is when the porcelain end of the probe cracks. Sometimes the crack is visible, but other times the damage may not be obvious until the sensor is replaced.

What A Heating Repair Technician Can Do

If the metal end of the probe is coated with debris, the technician can use emery cloths or a wire brush to gently remove the buildup. When the probe is cleaned, the sensor is replaced and the furnace started to see if it keeps running or if it shuts down again.

If the furnace still shuts down, the repair technician will probably change the sensor. Also, if the porcelain part of the sensor is cracked or chipped, the sensor needs to be replaced. The cost of replacing a flame sensor varies quite a bit depending on the brand of furnace you have. Even though the sensor is small, it's important and your furnace won't work unless it's operating properly. So, when the sensor goes bad, it has to be replaced. For more information, contact a heating repair service.