Furnace short cycles, turning on and off frequently without reaching the thermostat setpoint.

Safety first: Turn off power before opening panels.

• 1. Replace air filter: A clogged filter can cause overheating and limit trips. Install a clean filter of the correct size and rating for your Thermia furnace.
• 2. Check vents: Ensure all supply and return vents are open and unobstructed to improve airflow.
• 3. Evaluate thermostat location: If the thermostat is near a supply vent, in direct sun, or near appliances, it may sense heat too quickly. Consider relocating it to an interior wall in a representative room.
• 4. Observe furnace operation: Watch for the burners shutting off while the blower continues, then restarting soon after. This pattern suggests limit switch cycling. Have a technician check duct sizing, blower speed, and the high limit switch.