Marey electric tankless heater shows F5; unit may partially heat or not heat at all.

Safety first: Turn OFF all breakers feeding the heater. Confirm power is off before touching internal wiring.

Steps:

• Inspect element terminals: Remove the cover and visually inspect the heating element terminals for signs of burning, discoloration, or loose screws. Tighten connections if loose.
• Test elements (if you have a meter): Disconnect wires from each element and measure resistance across the terminals. An open circuit indicates a failed element that must be replaced.
• Replace faulty element: Shut off water, drain the unit if necessary, and remove the defective element. Install a new Marey-compatible heating element with proper gaskets.

When to call a technician: If multiple elements are out or if the control board’s switching devices are suspected.