When a furnace stops working, it is not always because some big or complex part has broken. Often, furnace failure can be blamed on a small, but vital, component. One component that tends to fail from time to time is the flame sensor. This part is meant to detect whether there is a flame on the burner and open the gas valve if there is. If there is no flame, the flame sensor will keep the gas valve closed so you don't get a gas leak.

So, what are the signs your flame sensor has stopped doing its job? Take a look. 

A Yellow or Orange Flame

Your furnace should burn with a white or blue flame. If the flame is yellow or orange, that means it is cooler than usual. This should not happen. The flame sensor should register the lower temperature and adjust the flow of gas accordingly. There are a few reasons why a furnace may have a yellow flame, but one of them is a broken flame sensor that's allowing more gas than it can burn.

Higher Energy Bills

Have your gas bills recently increased, even though the weather has not gotten colder? This could be because the flame sensor is not shutting off the flow of gas as it should. Not only can this be dangerous and lead to gas leaks, but it is also a waste of gas. So, have an HVAC contractor come take a look.

No Heat

Sometimes if a flame sensor fails completely, your furnace will just stop heating. The gas valve is not opening to feed the burner, so there is nothing to generate heat. It might take you a few hours to realize what's going on because the furnace fan may still run. But if you put your hand in front of the vent, you'll realize the air that's coming out is cool, not warm.

If the flame sensor is still working to some degree, the air that comes out may be warm, but not hot. Your furnace may keep running and running without your home ever reaching the setting on the thermostat.

Flame sensor problems should never be ignored. But the good news is that this is a common problem that HVAC contractors address regularly. The flame sensor is a relatively small and inexpensive part that they can remove from your furnace and replace. You'll have good, safe heat again in no time.

Contact a local HVAC service to learn more about heating repair.