Marey tankless water heater powers on but does not ignite; display shows E0 shortly after opening a hot water tap.

Safety first: Turn OFF the circuit breaker (or unplug if corded) and close the cold-water supply valve before opening the unit. Allow hot water lines to cool.

Steps to check and clear flow issues:

• Verify water supply: Make sure the main cold-water valve to the heater is fully open. Check that other fixtures in the house have normal pressure.
• Clean inlet filter: Shut off water to the heater. Remove the cold-water inlet connection at the bottom of the Marey unit. Locate the small mesh filter screen inside the inlet. Rinse debris under running water and brush gently. Reinstall the filter and reconnect the line.
• Check minimum flow: Open a hot tap fully. Many Marey tankless models require ~0.5–0.8 GPM to activate. If you have low-flow aerators or showerheads, temporarily remove them and test again.
• Inspect flow sensor: With power OFF and water OFF, remove the front cover. Locate the flow sensor/flow switch assembly on the cold inlet manifold. Check for scale buildup or stuck turbine/rotor. If the rotor does not spin freely or the reed switch wiring is damaged, the flow sensor assembly should be replaced.
• Reset and test: Restore water, then power. Open a hot tap and see if the E0 clears. If the error persists after cleaning and verifying flow, replace the flow sensor assembly.

When to call a technician: If you are not comfortable opening the unit or working around water and electricity, or if the flow sensor wiring needs testing with a multimeter, contact a qualified technician.