Navien E004: false flame detection

Before a tankless heater lights, it checks that no flame is present. If the flame sensing circuit reports a flame when there should be none, the unit refuses to start and shows E004.

In most cases there is no actual fire where it should not be. The control board is reading a stray electrical signal, which is why grounding is the first thing Navien asks you to check.

The meaning below comes from Navien's manuals for its NPE condensing tankless water heaters. Many codes are shared with Navien combi boilers, but check the manual for your model if something does not match.

What to check

1. Make sure the heater is plugged into a properly grounded three-prong outlet, not through an adapter that drops the ground.
2. Check whether the code started after electrical work, a storm or a power outage.
3. Reset the unit once from the front panel.

What a technician checks

Navien's service manual lists checking the ground wire, checking the power supply and tightening the ground connection screws on the heat exchanger. A loose ground screw or a damaged ground wire can let stray voltage confuse the flame sensor.

How to reset a Navien

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

If E004 returns, leave the unit off and call a licensed installer.

See every code on our Navien error codes page.