Ariston instant electric water heater runs but water temperature fluctuates rapidly (hot-cold-hot).

Safety first: Turn off power before opening the unit.

• Adjust flow: Reduce the flow at the tap or install a flow restrictor to keep flow within the heater's rated range.
• Clean inlet filter: Remove and clean the cold inlet filter to ensure stable flow.
• Check power and phases: Verify that all required phases are present and that the heater is wired correctly.
• Inspect flow sensor: Clean or replace the flow sensor if it is sticking or giving erratic readings.