A gas furnace relies on a carefully controlled ignition system to start the heating cycle and maintain a steady flame. When something goes wrong with this process, the furnace may start briefly and then shut down, or it may fail to ignite at all.
For homeowners in the Comox Valley, ignition problems are one of the more common causes of furnace service calls during the heating season. Understanding the possible causes can help you recognize when it’s time to call a professional.
Understanding How Furnace Ignition Works
Modern gas furnaces use one of two ignition systems. Older systems rely on a standing pilot light, while most newer furnaces use an electronic ignition system.
Electronic ignition furnaces typically use either a hot surface igniter or an intermittent pilot to light the burners. Once the flame is detected, the furnace continues the heating cycle. If the system does not detect a proper flame, it will shut down as a safety precaution.
When this process fails, the furnace may attempt to start several times before shutting off completely.
Dirty or Faulty Flame Sensor
One of the most common causes of ignition failure is a dirty flame sensor. This small metal rod confirms that the burner flame is present.
If the sensor becomes coated with carbon buildup or dirt, it may fail to detect the flame even though the burner has ignited. As a result, the furnace shuts down within a few seconds.
Cleaning or replacing the flame sensor is a routine repair for HVAC technicians.
Worn or Failing Igniter
In furnaces that use a hot surface igniter, the igniter must glow red-hot to light the gas burners. Over time, these components can become brittle and eventually fail.
When this happens, the furnace may attempt to start but never produce a flame. Igniters are delicate parts that must be handled carefully and replaced by a trained technician.
Gas Supply Problems
Ignition issues can also occur if the furnace is not receiving enough gas. A partially closed gas valve, supply interruption, or pressure problem can prevent the burners from lighting properly.
Because gas systems involve safety risks, homeowners should never attempt to diagnose gas supply problems themselves.
Blocked or Dirty Burners
Burners that are clogged with dust or debris may prevent proper ignition. If the gas cannot flow evenly through the burner ports, the flame may not establish correctly.
Regular furnace maintenance helps keep burners clean and operating safely.
Why Professional Diagnosis Matters
Gas furnaces are equipped with safety systems designed to shut the unit down when something isn’t working correctly. While this protects your home, it also means the root cause of ignition problems may not always be obvious.
Professional technicians have the tools and training to inspect ignition components, test sensors, and ensure the furnace is operating safely.
Final Thoughts
If your furnace starts but won’t stay lit, the ignition system may be struggling to complete the heating cycle. Addressing the issue early can prevent repeated shutdowns and restore reliable heat.
If you’re experiencing furnace ignition problems, contact KL Mechanical. Our experienced technicians provide professional furnace repair and diagnostics throughout the Comox Valley, helping homeowners keep their heating systems running safely and efficiently.