What does error code E016 mean on a Navien tankless water heater?

Heat exchanger overheating. The heat exchanger is overheating.

Can I fix Navien code E016 myself?

Start with these safe checks: Clean the cold water inlet filter as the manual shows (shut off water first). Flush the heat exchanger, or have a plumber do it. If it continues after flushing, contact Navien technical support.

When should I call a technician for code E016?

If it continues after flushing, contact Navien 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 E016: Heat exchanger…

What E016 means

The heat exchanger is overheating.

Likely causes

Clogged cold water inlet filter
Scale in the heat exchanger

Safe first checks

Clean the cold water inlet filter as the manual shows (shut off water first).
Flush the heat exchanger, or have a plumber do it.

When to stop

If it continues after flushing, contact Navien 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.