Navien furnace intermittently shows E127, especially during very cold weather

Safety: Turn off power before working on the condensate system. Condensate is mildly acidic; wear gloves and eye protection.

• Inspect condensate trap: Locate the clear or opaque plastic trap at the bottom of the unit. Check for sludge, debris, or standing water that does not drain. Remove the trap if possible and flush thoroughly with clean water.
• Check drain line: Follow the drain hose to its termination. Ensure it is not kinked, frozen, or routed uphill. Correct the slope so condensate flows freely to the drain.
• Insulate or heat trace (if needed): In cold climates, insulate exposed condensate lines or install heat trace cable per code to prevent freezing.
• Inspect for leaks or cracks: Examine the trap and fittings for cracks or leaks. Replace the trap assembly if damaged.
• Reset and monitor: Restore power, reset the unit, and observe condensate flow during operation. If E127 recurs, have a technician verify the internal condensate level sensor or pressure switch.