Flame Sensor, Igniter, Or Something Else — Why Won't Your Furnace Light?


A natural gas furnace must work through several steps before it can successfully and safely ignite. The final step in the ignition process is known as flame rectification. During this step, the furnace proves that all its burners have ignited, ensuring that unburnt gas isn't escaping into the furnace cabinet and your home.

The ignition process itself involves several steps. Once the igniter turns on, the gas valve opens and releases gas to the burners. The control board will then wait for the burners to ignite and attempt to sense the flame. If the flame sensor can't detect heat from the final burner, your furnace's gas valve will close, and the furnace will shut down.

Recognizing Ignition Problems

Recognizing an ignition problem with your furnace can be tricky since it often seems like your furnace isn't doing anything. As with most furnace problems, start by turning your thermostat's setpoint up a few degrees and waiting to see what happens. The thermostat should begin demanding heat relatively quickly, causing the furnace to start its ignition sequence.

Standing near your furnace, you should be able to hear several things happening once the startup sequence begins. You'll usually hear the draft inducer (a small fan) turn on first. If you can hear this sound after adjusting your thermostat, it successfully signaled for heat, and your furnace is ready to fire up.

The next sound should be the woosh of gas followed by the burners igniting. If you can hear the burners quickly ignite and then shut off, there may be an issue with the flame sensor or one or more burners may not be fully igniting. If you hear nothing or your gas valve quickly clicks open and closed, it likely means your igniter has an issue.

Resolving Furnace Ignition Problems

Although there are typically a relatively small number of culprits for a furnace ignition problem, each has a crucial role in safely igniting your furnace. Guessing the problem or blindly replacing parts can waste money or leave your furnace in a potentially unsafe state. Without proper ignition and flame rectification, your furnace can operate inefficiently or release hazardous unburnt gas into your home.

If you suspect your furnace may have an ignition problem, your first step should always be to contact a skilled HVAC technician. A technician will verify each step of your furnace's ignition sequence, checking for problems with your furnace's igniter, flame sensor, burners, and more. This in-depth diagnosis is critical to repairing your ignition problem and ensuring your furnace can operate safely. 

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


22 February 2023

Learning About HVAC Services

Hi there, I am Nadine Bachmier. I am going to discuss the various ways HVAC contractors can keep the temperatures in your business stable. HVAC contractors focus on maintaining and repairing the air conditioner, furnace, and ductwork used in your building. To keep the heating and cooling system in good shape, contractors may need to replace internal components, clean out channels, or simply perform a full upgrade. I will talk about the tools and techniques used to maintain and repair the equipment in your building. I will also share information about new products as they hit the HVAC market. I hope you will follow along and learn all you can.