What does error code E439 mean on a Navien tankless water heater?

Flow sensor fault. Abnormal operation of the flow sensor.

Can I fix Navien code E439 myself?

Start with these safe checks: Note the code. Navien says contact technical support.

When should I call a technician for code E439?

Navien says contact technical support. Smell gas? Leave right away, don't touch light switches or phones inside, and call your gas utility or 911 from outside. Never open a gas valve, burner, gas line, vent or flue connection, or bypass a safety switch. Repeated lockouts, scorching, soot, or a CO alarm mean shut it off and call a licensed gas technician.

Navien tankless water heater error code

Navien tankless water heater code E439: Flow sensor fault

Navien NPE-2 tankless water heaters

What E439 means

Abnormal operation of the flow sensor.

Likely causes

Flow sensor fault

Safe first checks

Note the code.

When to stop

Navien says contact technical support.

Checked against: Navien NPE-2 user's information manual: understanding error codes. Codes can differ by model and year, so confirm with your owner's manual.