Display shows E04, furnace stops heating, may restart after cooling down.

Safety: Switch off power. Allow the furnace to cool completely before touching internal components.

• Check air filter and vents: Replace or clean the return air filter. Ensure all supply and return grilles are open and not blocked by furniture.
• Verify circulation fan operation: Set the thermostat fan to ON. If the blower motor does not run, check the Termet control board fuse and blower motor connections. Listen for humming or grinding.
• Inspect high-limit thermostat: Locate the high-limit thermostat on the heat exchanger panel. Check for loose wiring. Many Termet limits are manual-reset; press the reset button if present.
• Check for dust buildup: Vacuum dust from the blower compartment and around the heat exchanger to improve airflow.

Professional help: If E04 recurs, a technician should inspect the heat exchanger for internal blockage, verify blower speed settings, and test the high-limit thermostat.