Furnace displays E19; unit may shut down on condensate-related fault

Safety first: Turn off power. Condensate may be mildly acidic; wear gloves and eye protection.

• Locate condensate system: Find the condensate trap on the furnace and the PVC drain line leading to a floor drain or condensate pump.
• Clear trap and line: Remove the trap and flush thoroughly with warm water. Use a wet/dry vacuum at the end of the drain line to pull out sludge or algae.
• Check float switch: If a condensate pump is used, inspect the pump reservoir. If full, the float switch may be open. Clean the pump, ensure the discharge line is clear, and test pump operation.
• Verify slope: Ensure the drain line slopes continuously downward with no sags that can trap water.
• When to replace: Replace a failed condensate pump or float switch if they do not operate correctly after cleaning. Persistent E19 after clearing the system may indicate a wiring or board input issue.