How to Fix / Troubleshooting

Safety first: Turn off power and close the water supply valve.

Clean inlet filter: Disconnect the cold inlet connection and remove any mesh filter. Rinse under running water to remove debris and reinstall.
Access flow sensor: On Ariston instant heaters, the flow sensor is usually located on the cold inlet manifold. Remove the cover and locate the sensor housing.
Inspect and clean turbine: Carefully open the flow sensor housing (if serviceable) and remove limescale or debris from the turbine/rotor. Ensure it spins freely.
Check wiring: Verify the sensor connector is firmly seated on the control board and that the cable is intact.
Replace flow sensor: If the sensor is electrically open or physically damaged, install a new Ariston-compatible flow sensor assembly.

Restore water supply, check for leaks, then restore power and test by opening a hot tap. The E10 code should clear when proper flow is detected.

Ariston instant electric water heater shows E10 and does not start heating when tap is opened.

Possible Causes