Navien E047: exhaust sensor fault

Navien heaters watch the temperature of the exhaust gases to protect the vent pipe and the unit. The sensor that does this is the exhaust thermistor. E047 means the reading from that sensor makes no electrical sense: either no circuit at all (open) or a dead short.

Navien's service manual splits E047 into two sub-codes: one for an open thermistor and one for a shorted thermistor.

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.

For this code, Navien's user manual directs owners to contact Navien technical support (1-800-519-8794) or a licensed installer.

Common causes

• A loose connector at the sensor or at the control board
• A wire damaged by heat, vibration or rodents
• Moisture or corrosion at the connector
• A failed sensor

What happens next

A technician checks the connections at both ends and measures the sensor. If the wiring is sound and the sensor reads open or shorted, it is replaced. It is an inexpensive part and a fairly quick repair.

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 E047 comes straight back, the sensor circuit still has a fault. Leave the unit off and schedule service.

See every code on our Navien error codes page.