Bosch tankless water heater shows A3; the unit may derate or shut down intermittently.

Safety first: Turn OFF power and close water valves before removing filters or sensors.

• Clean inlet filter: Remove and rinse the cold water inlet filter screen to restore full flow.
• Check household plumbing: Ensure that faucet aerators and showerheads are not severely restricted. Clean or replace if necessary.
• Inspect flow sensor: Remove and clean the water flow sensor turbine. Ensure it spins freely and is free of scale.
• Verify minimum flow: Some Bosch models allow adjustment of minimum activation flow. Refer to the manual to ensure it is not set too high for your fixtures.
• Test operation: Restore water and power, then run multiple hot water fixtures to confirm stable operation.