Furnace shows C2; burner shuts down during operation

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Partial flue blockage, Condensate backing up into flue, Weak combustion fan, Intermittent air pressure switch

Safety: Shut off power and gas before inspection.

Condensate system: Remove and clean the Bosch condensate trap. Flush with water and reassemble. Ensure the drain hose is not kinked or frozen.
Flue inspection: Check for sagging horizontal runs where condensate can pool. Correct slope and support as needed.
Switch and tubing: Replace any suspect tubing. If the switch shows signs of moisture inside, replace it.

If C2 recurs, a technician should measure fan pressure and verify correct flue sizing and installation.

Hard 4/5

Air Pressure Switch

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