Marey electric tankless heater shows F1 and does not heat; water flows but remains cold.

Safety first: Turn OFF the circuit breaker(s) feeding the heater. Verify with a non-contact tester that power is off before opening the cover.

Steps:

• Access sensors: Remove the front cover. Locate the inlet temperature sensor on the cold water side (often clipped or threaded into the inlet manifold).
• Check connection: Ensure the sensor plug is firmly seated on the control board and that the wire is not cut or pinched.
• Replace sensor if faulty: If the sensor is physically damaged or tests open/short with a meter, shut off water, relieve pressure, and replace it with a Marey-compatible inlet NTC sensor.

When to call a technician: If you are not comfortable working inside an electric heater or if replacing the sensor does not clear the F1 code.