6 Reasons Why Your Furnace Won’t Ignite

Most homes use a furnace to create and distribute heat. Furnaces are designed to last 15 to 20 years before needing to be replaced. Sometimes a furnace won’t ignite because the system won’t light the burners that provide heat. If your furnace is less than 15 years old and won’t ignite, check for any underlying problems before seeking a full replacement.

Why Won’t My Furnace Ignite?

Your furnace won’t ignite due to one or more of the following reasons:

1. Gas Line Issues

The source of your malfunctioning furnace may be related to gas line issues. Common types of natural gas issues include gas leaks, blocked gas lines, and malfunctioning gas valves. If the gas line is off, simply turn it back on. If the furnace won’t ignite after doing this, call an HVAC professional to check for other potential problems. If you smell gas at any point, exit your home and notify your gas company.

2. Defective Thermostat

For your furnace to ignite, the thermostat must be set on heat mode. If it’s not, your furnace won’t ignite the burners. Another possibility is that the thermostat’s connections or sensors are faulty. First, make sure the thermostat is set to heat mode. If the issue persists, get professional help.

3. Dirty Furnace Filter

When furnace filters aren’t replaced frequently, they collect dust and other particles. Dirty HVAC filters prevent proper airflow which is necessary to ignite the burners. Replace your furnace filter roughly every few months.

4. Malfunctioning Igniter or Pilot Light

Sometimes furnaces that use a standing pilot light to ignite burners won't stay lit, or the light goes out completely. In furnaces that have an electronic system to ignite burners, a dirty or burned igniter can prevent the burners from igniting. For any of the problems listed above, contact an HVAC technician for assistance.

Tips & Insights: Ways To Repair a Malfunctioning Heating System

5. Broken Flame Sensor

If your furnace won’t ignite, the source of the issue may be a broken flame sensor. The sensor is responsible for turning off the gas burners to avoid gas buildup. Once this component starts to malfunction, it may stop the burners from igniting altogether. If this problem occurs, you have two options:

• Replace the flame sensor yourself

• Have an HVAC technician replace the flame sensor

6. Dirty Gas Burners

If burners are dirty, they can’t bring in the oxygen necessary to ignite them. Contact a professional to remove, clean, and return the burners.

3 Types of Furnace Ignition Systems

Learn about the 3 main types of furnace ignition systems:

1. Standing Pilot Light

The gas valve knob on furnaces with a standing pilot light system read "OFF/ON/PILOT." This system contains a thermocouple, which is a heat-sensing tool. The thermocouple ensures that gas reaches the burners only when the pilot light warms the thermocouple.

2. Intermittent Pilot Igniter

The intermittent pilot igniter is one kind of electronic ignition system. Like the standing pilot light, the intermittent pilot igniter uses a pilot flame. The difference between the two is that the pilot flame in the intermittent pilot igniter comes on only when the thermostat signals the heat to turn on. Here’s how the process works:

• An electronic control board signals an igniter

• The igniter turns on the pilot flame

• The pilot flame turns on the gas

• After the burn cycle finishes, the burners and pilot flame deactivate

3. Hot Surface Ignition

Hot surface ignition systems contain a hot surface igniter (HSI). The HSI includes a fork-like attachment, a plastic base, and two wires. When the thermostat signals heat to turn on, the fork attachment becomes hot. This temperature increase signals the gas valve to open, igniting the gas.

Superior Furnace Repair & Replacement Services

If your furnace won’t ignite, contact your local furnace experts at Horizon! Our technicians provide customers with same-day emergency furnace repair and furnace installation services. Our professionals offer heating repair services in Trenton, NJ and other areas. When you find yourself in a tight spot and don’t know what to do, we’re here to fix the problem and put your mind at ease. Learn more about when to call for furnace repairs on our website, or call us at (800) 642-4419 to speak with a technician.