hot surface ignitors are found on most modern furnaces to light the gas
flames upon unit start-up. Electricity passes through the Silicon
Carbide or the newer Silicon Nitride ignitor and makes it glow red hot.
Operating under normal conditions a hot surface ignitor will last for 3
to 5 years (Silicone Nitride lasts about twice as long). During that
time ignitors will eventually crack and need to be replaced. Like a
light bulb, they are a regular replacement item. Most ignitors are
interchangeable as long as they fit in the furnace space provided.
1. Verify that all wire connections are secure from the
furnace to the hot surface ignitor.
2. Does the hot surface ignitor have any
visible abnormal spots on it.? A burned hot surface ignitor will
typically have a white or burned spot when it has failed. The below hot
surface ignitor failed due to a "bad spot."
3. Does the hot surface ignitor glow when the furnace cycles?
4. You will need a multimeter to check the
power of the hot surface ignitor. Disconnect the plug going to the
ignitor. Use your Multimeter to see if you have 115 volts. Make sure you
do this on startup of Heating unit. After a minute or so it will be
times out. Then you will have to shut the heating system off and then
turn it back on again.
A. You will need a multimeter to check the
resistance of the hot surface ignitor. A hot surface ignitor uses
resistance just like a light bulb to glow hot in order to light the gas.
It typically has a life span of 2 to 3 years depending on the usage and
the conditions of the furnace. Set the multimeter so it can
properly measure a resistance of 10 to 200 ohms. Disconnect the
hot surface ignitor from the control board and measure the resistance.
A good hot surface ignitor will have a resistance of 40 to 90 ohms.
Greater than 90 ohms indicates a failing or failed hot surface ignitor.
5. If your hot surface ignitor is good,
then you need to verify power from the control board or ignition
controller. Disconnect the hot surface ignitor and measure the
voltage coming from the controller. A good reading is 115 to 120
VAC. If there is no voltage and the furnace is cycling for a call
for heat, then the furnace control board or ignition controller needs to
6. Cross - Reference and Upgrade Replacement Guide