Furnace shows E16, heating stops, sometimes after long operation.

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

Steps:

• Inspect condensate trap: Locate the plastic condensate trap at the bottom of the heat exchanger. Remove it according to the manual and flush with clean water to remove sludge and debris.
• Check drain hose: Ensure the hose from the trap to the drain is not kinked, blocked, or frozen. Clear any blockage and re-establish proper slope.
• Check condensate switch: Some Cointra furnaces use a float or level switch. Verify that it moves freely and that wiring is intact.

Professional help: If E16 persists, a technician should inspect the internal condensate channels and replace the level switch if faulty.