Navien E445: mixing valve fault

Navien heaters use a mixing valve to blend cold water into the heated water. This helps prevent temperature spikes and keeps the outlet steady. E445 means the valve is not responding the way the control board expects.

The meaning below comes from Navien's manuals for its NPE condensing tankless water heaters. Navien directs owners to its technical support line (1-800-519-8794) or a licensed installer for this code.

What you might notice

• Hot water that swings between too hot and lukewarm
• The heater shutting down with E445 during use

Common causes

• A failed valve motor
• Loose or damaged wiring
• Scale or debris affecting the valve in hard water areas

What you can do

Reset the unit once. If E445 returns, schedule service. Keeping up with flushing and cleaning the inlet filter reduces the chance of scale affecting valves.

How to reset a Navien

1. Close all hot water taps.
2. Turn the unit off with the power button on the front panel, wait about a minute, then turn it back on.
3. Open a hot tap and watch whether the code returns.

Before you call

Have the model and serial number from the rating label ready, along with the exact code and when it appears: at startup, during use, or only at high demand. Mention any recent work on the gas, water or electrical supply and when the heater was last descaled. This helps the technician bring the right parts and often saves a second visit.

See every code on our Navien error codes page.