Furnace attempts to start but shuts down quickly, display shows E02, inducer may run briefly.

Safety first: Turn off power to the furnace. Do not operate the furnace if you suspect a flue blockage or exhaust leak—risk of carbon monoxide.

• 1. Inspect venting system: From the furnace to the outside termination, check the exhaust and combustion air intake pipes used by the Thermia furnace. Look for ice, leaves, nests, or debris blocking the PVC vent or intake. Clear any obstructions.
• 2. Check condensate drain (if condensing model): A clogged condensate trap or drain line can cause water to back up into the inducer and pressure switch tubing. Inspect the Thermia condensate trap assembly and hoses; flush with warm water and ensure proper slope and drainage.
• 3. Inspect pressure switch tubing: Locate the pressure switch near the inducer housing. Remove the silicone or rubber tubing and check for water, cracks, or kinks. Blow through the tubing to clear any blockage and reinstall securely on both the pressure switch and inducer port.
• 4. Test pressure switch operation: With power off, disconnect the wires from the pressure switch and check continuity with a multimeter. When the inducer is running (power on, call for heat), the switch should close. If it never closes despite good draft and clear tubing, replace the pressure switch with a Thermia-specified replacement.
• 5. Inspect inducer motor: Check that the inducer fan wheel spins freely and is not obstructed. Listen for grinding or humming when it runs. If the inducer fails to start or is very weak, the inducer assembly may need replacement.
• 6. Reset and test: After clearing blockages and verifying components, restore power and call for heat. If E02 persists, contact a qualified technician to measure draft and verify correct operation of the Thermia combustion system.