Furnace shuts down when access panel is slightly bumped or moved.

Safety first: Turn off power before adjusting switches or wiring.

Steps:

• Inspect the CTC blower door safety switch and ensure it is firmly mounted and properly aligned with the door.
• Adjust the door panel so it fully depresses the switch when closed; add shims if necessary.
• Check low-voltage wiring connections at the control board for tightness.
• If the switch is loose internally or intermittent, replace it.