Marey electric tankless heater displays F4 and shuts down; may occur under high demand.

Safety first: Turn OFF power at the breaker and close the water supply. Wait for the unit to cool completely.

Steps:

• Reset high-limit: Remove the cover and locate the manual reset high-limit thermostat on the heating chamber. Press the reset button if present until it clicks.
• Check for restrictions: Ensure inlet filter, outlet valves, and fixtures are not clogged. Clean aerators and showerheads.
• Descale heating chamber: If you have hard water, perform a descaling flush through the electric heater using a pump and descaling solution, following Marey guidelines.
• Lower temperature setting: Reduce the set temperature to decrease stress on the elements.

When to call a technician: If the F4 code returns frequently, the high-limit or control board may need replacement.