Furnace will not start, no burner ignition, display shows E01 shortly after a call for heat.

Safety first: Turn off electrical power to the furnace at the breaker and close the gas shutoff valve before touching any internal components. Allow the furnace to cool completely.

• 1. Verify thermostat call for heat: Set the thermostat several degrees above room temperature. Confirm that the furnace receives a call for heat (you should hear a relay click or see the inducer attempt to start).
• 2. Inspect the hot surface igniter: Remove the burner access panel. Locate the hot surface igniter near the burners. Check for visible cracks, white spots, or breaks in the ceramic. If damaged, replace the igniter with a Thermia-compatible hot surface igniter rated for your model.
• 3. Check igniter resistance: With power off and wires disconnected, measure resistance across the igniter terminals using a multimeter. Typical values are 40–200 Ω (consult Thermia service documentation). If open (infinite resistance) or far out of spec, replace the igniter.
• 4. Inspect flame sensor: Locate the flame sensor rod at the burner. Remove it and gently clean the metal rod with fine steel wool or a Scotch-Brite pad to remove oxidation. Reinstall and ensure the sensor is properly positioned in the burner flame path.
• 5. Confirm gas supply: Make sure the manual gas shutoff valve to the furnace is fully open (handle parallel to the pipe). If other gas appliances are not working, contact your gas supplier. Do not attempt to adjust gas pressure yourself.
• 6. Check wiring to ignition control module: Inspect harnesses from the main control board/ignition control module to the igniter and flame sensor. Look for loose connectors, corrosion, or heat damage. Reseat connectors firmly.
• 7. Test operation: Restore power and gas, then call for heat. Observe the sequence: inducer starts → igniter glows → gas valve clicks → burners light. If the igniter never glows or the system locks out again with E01, the ignition control module or main control board may be defective and should be tested/replaced by a qualified technician.