Testing Your Furnace Igniter

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It can be shocking how quickly the moderate autumn temperatures can turn downright frigid which can have you thinking about firing up your furnace a lot sooner than you anticipated. While there is regular maintenance you should be doing to keep your gas furnace running optimally, it’s always a good idea to test the furnace out early every fall to confirm all the components are functioning properly. Since the number one cause of a gas furnace not heating is a faulty igniter, you’ll want to make sure the furnace igniter will operate as expected before the cold weather requires you to use the furnace on a daily basis.

Understanding how a gas furnace igniter works

By understanding how a gas furnace igniter works with all the other components to successfully initiate the furnace’s timed ignition sequence, you’ll be in a better position to determine if a broken igniter is the cause of the furnace not heating.

How a gas furnace’s timed ignition sequence begins

The furnace ignition sequence begins when the home’s thermostat calls for heat, prompting the circuit board to send 120 volts of alternating current to the furnace’s draft inducer fan motor. The inducer fan motor draws air into the burner assembly and, when the fan motor reaches its maximum speed, a pressure switch is closed to ensure that gas will not enter the furnace unless the toxic fumes generated by the combustion process can be exhausted safely. Once the pressure switch closes, 24 volts will travel through the switch, and one or more limit switches, allowing the circuit board to continue the combustion sequence.

Glow-bar style igniter vs. spark igniter

The next step in the sequence has the circuit board sending voltage to the igniter. Depending on the furnace model, the igniter may be a glow-bar style igniter or a spark igniter. While the circuit board will send 120 volts of alternating current to a glow-bar style igniter, it will normally send an even greater amount of voltage to a spark igniter. The glow-bar style igniter will begin to heat up and will literally begin to glow orange, whereas a spark igniter will begin to pulse to create a spark. As this happens, the circuit board will send 24 volts to the gas valve, opening it and allowing gas to flow over the igniter where the gas is ignited into a flame.

How can you tell if a furnace igniter is defective?

If a glow-bar style igniter doesn’t heat up or a spark igniter fails to produce a spark, it’s likely the igniter is too weak to ignite the gas or it may lack the necessary electrical continuity to function properly. How can you tell if the igniter is defective? You should first inspect the component for cracks in the element or base as this is a strong indicator that the part is faulty. You can also use a multimeter to test a glow-bar style igniter.

Using a multimeter to test a glow-bar style furnace igniter

A multimeter can be used to help determine if a glow-bar style furnace igniter has sufficient electrical continuity – a continuous electrical path present in the part – for the igniter to function properly. Here are the steps you should follow to test the igniter:

  • Rotate the multimeter’s range selection dial to the lowest setting for Ohms of resistance. If you’re using an analog meter, be sure to calibrate the meter by pinching the meter leads together while adjusting the needle to read “zero”.
  • When testing the igniter, shut off the power to the furnace and detach the power wires from the igniter terminals or disconnect the power wire connector. Be careful not to damage the igniter’s filament when doing this.
  • Touch the black (negative) lead to one of the igniter’s terminals and the red (positive) lead to the other terminal (if the power wires use a connector housing, the two terminals will located be side-by-side in the housing).
  • If the meter display indicates a result between 20 and 400 Ohms of resistance, the igniter has good electrical continuity and should be fully functional.
  • If the meter display shows a higher result than 400 Ohms of resistance, it’s likely the igniter has weakened; a fully negative continuity result will mean the part has failed completely.

If the igniter appears to be in good shape and shows good electrical continuity, then it’s probable one of the other ignition sequence components is at fault and you’ll need to continue troubleshooting. A weakened furnace igniter, or one that has no electrical continuity, will need to be replaced with a new one.

Learning how to replace the furnace igniter

As with testing the igniter, you should always shut off the power to the furnace before you attempt to install a new igniter or any other furnace component. You will usually need to remove one or both of the furnace’s combustion panels to access the igniter. Once you detach the power wires from the igniter terminals or disconnect the wire connector, you can usually unthread a single screw securing the igniter to fully remove it. While the installation of a new igniter can be as simple as aligning the new component in the burner housing, securing it with the mounting screw, and connecting the wire connector (or connecting the power wires to the individual terminals), the exact installation procedure will vary from model-to-model.

To see model-specific information, step-by-step part replacement guides, and procedural videos, you should enter the full model number of the furnace in Repair Clinic.com’s “Videos & Articles” section. Repair Clinic can show you the precise method for installing that new igniter, including how to replace a York gas furnace (Model TG9S080B12MP11A) igniter with a compatible universal igniter.

Repair Clinic stocks genuine OEM igniters and other furnace parts

While universal igniters are available, it is strongly recommended that you replace the old igniter with a new one that is specifically designed to work with your furnace model. Repair Clinic. com makes it easy to find the right part. All you need to do is enter the full model number of the furnace in the website’s “Search Parts Online & Get Answers” section, then select “Igniter” using both the “Part Category” and “Part Title” filters to locate the exact igniter that works with your furnace. Importantly, all of the furnace parts on the Repair Clinic site, including igniters, flame sensors, pressure switches, draft inducer fan motors, gas valves, or control boards, are genuine OEM replacement parts, direct from such manufacturers as Bryant, Lennox, Goodman, Rheem, York, Coleman, Ruud, Heil, or Payne. It’s one more reason to trust Repair Clinic as your repair partner when you need to fix your heating and cooling products.

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