How to troubleshoot a Hot Surface Ignitor (HSI)
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 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. Search for a replacement HSI.
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 replaced. Search for a furnace control board.
*This guide's intention is to provide an understanding of the operation of a furnace. It is not intended as a hands-on teaching tool, or aide. All HVAC equipment should be serviced by a licensed HVAC technician. Consult your local, town, city, and state laws, oridinances, and regulations prior to accessing, engaging, troubleshooting, repairing, or servicing any HVAC equipment.
SAFETY NOTE - ALWAYS TURN THE MAIN POWER AND GAS VALVE OFF BEFORE SERVICING ANY HVAC EQUIPMENT. SERIOUS INJURY CAN OCCUR.