Navien tankless water heater code E170: Freeze protection heater fault

Tankless water heater, United States

The electric heater that protects the unit from freezing has an open or short circuit.

This needs a licensed gas or HVAC technician. There is nothing safe to check yourself. Leave the covers on and book a professional.

What causes it

The freeze protection heater or its wiring has failed. Navien lists no owner fix for this code.

Book a licensed gas or HVAC technician

Have the model number, serial number, purchase date, where the heater is installed and the error code ready.
Call Navien Technical Support on 1-800-519-8794, or contact the company that installed the heater.
For a repair under warranty, the installer or service provider must contact Navien before starting the work.

Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
Note the code, how often it appears, and the model and serial numbers from the rating label.
Book a licensed gas or HVAC technician and give them those details.

7 models in 2 ranges

Range	Models
NPN-E	NPN-120E, NPN-160E, NPN-180E, NPN-199E
NPN-U	NPN-160U, NPN-180U, NPN-199U

Checked against the manufacturer's manual on 9 October 2026.

Code	Meaning	What you can do
E056	Modulating gas valve fault	Call a pro
E060	Dual venturi fault	Call a pro
E109	Fan motor fault	Safe checks first, then a pro
E110	Abnormal air pressure (blocked vent or intake filter)	Safe checks first, then a pro
E127	Air volume sensor fault	Call a pro
E157	Air volume control fault	Call a pro
E407	Hot water outlet temperature sensor fault	Call a pro
E421	Cold water inlet temperature sensor 1 fault	Call a pro
E432	Cold water inlet temperature sensor 2 fault	Call a pro
E434	Water adjustment valve fault	Call a pro
E438	Circulation pump fault	Safe checks first, then a pro
E439	Flow sensor fault	Call a pro