Furnace starts and runs but shuts down when the hopper is half full or more.

Safety first: Turn off and unplug the furnace before inspecting the hopper and lid switch.

Steps:

• 1. Observe lid fit: When the hopper is full, check if the lid sits differently or fails to close fully. Adjust hinges or latches as needed.
• 2. Check hopper lid switch: Ensure the switch is fully engaged when the lid is closed, even with a full hopper. Adjust the switch position or lid striker.
• 3. Inspect for bridging: Fuel can bridge more easily when the hopper is full. Stir the fuel and ensure it flows freely to the auger.
• 4. Hopper deformation: If the hopper walls bow outward when full, they may affect the lid or switch. Reinforcement or replacement of the hopper may be required.