Furnace control shows low flame signal or unstable flame; intermittent heat.

Safety first: Turn off power and gas before cleaning burners or working near gas piping.

Steps:

• Remove the burner assembly access panel and visually inspect burners for rust, debris, or misalignment.
• Clean burner ports with a soft brush and compressed air. Do not enlarge burner openings.
• Verify that the CTC flame sensor is clean and properly positioned in the flame.
• Check the furnace ground wire from the control board to the cabinet and from the cabinet to the incoming electrical ground. Tighten any loose screws.
• Inspect the gas valve ground and wiring harness for secure connections.
• If issues persist, a professional should measure flame rectification current and gas manifold pressure and may need to adjust or replace the CTC gas valve or burners.