Water temperature fluctuates between hot and cold during a shower without any error code on the display.

Safety: Water may become very hot unexpectedly. Use caution when testing.

• Test with one fixture: Turn off other water-using appliances and test with a single shower or faucet fully open to see if fluctuations improve.
• Bypass mixing valves: If using a thermostatic shower valve, temporarily set it to full hot and adjust temperature only on the heater to see if stability improves.
• Clean filters and aerators: Remove and clean inlet filter, faucet aerators, and showerheads to ensure stable flow.
• Descale unit: In hard water areas, perform a descaling of the heat exchanger and clean temperature sensors to improve response.
• Adjust setpoint: Set a moderate temperature (e.g., 115–120°F / 46–49°C) and avoid mixing with cold at the tap. If fluctuations persist, have a technician check sensors and control calibration.