Bosch condensing tankless water heater shows EA and shuts down

Safety first: Turn OFF power to the heater. Condensate is mildly acidic; wear gloves and eye protection when handling.

• Inspect condensate trap: Locate the condensate trap at the bottom of the heat exchanger on condensing Bosch models (e.g., Greentherm, Therm C series). Check for overfilling, sludge, or debris. Remove and clean the trap per the manual, then refill with clean water before reinstalling.
• Check drain line: Follow the condensate hose to its termination. Ensure it slopes continuously downward with no kinks or sags. Clear any blockages and flush the line with water.
• Cold climate considerations: In unconditioned spaces, insulate the condensate line and ensure it does not terminate outdoors where it can freeze. Thaw any frozen sections carefully and correct routing.
• Level switch (if present): Some models use a float or level sensor in the trap. Inspect for free movement of the float and clean any buildup. Verify wiring connections.
• Test operation: Restore power and run the heater. If EA recurs, the condensate sensor or control board may require professional diagnosis.