On some Keeprite models, code 31 indicates pressure switch open during run; furnace may shut off mid-cycle.

Safety: Turn off power and gas before opening the inducer or vent connections.

Steps:

• Check for intermittent vent blockage: Inspect vent terminations for flapping debris, insect screens, or snow that could intermittently block flow.
• Inspect condensate drain: Ensure the condensate trap and hoses are clear and that water is not backing up into the inducer housing. Clean and flush as needed.
• Secure tubing: Make sure the pressure switch tubing is firmly attached and not vibrating loose during operation.
• Monitor inducer current draw: A motor drawing high current or slowing during run may be failing and should be replaced.

Because loss of draft can lead to unsafe operation, have a professional verify combustion and venting after repairs.