Navien E773 Error Code: Wrong gas
Updated October 2026 · Sourced from Navien documentation
🛑 Turn it off and call a licensed pro
The manual says the unit is using the wrong gas and tells you to contact customer support.
Is it safe to keep running? No. Turn it off and get it checked. Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
E773 at a glance
| Code / how it shows | Meaning | Applies to |
|---|---|---|
| E773 Error code shown on the front panel display | Wrong gas | NPE-180A2, NPE-210A2, NPE-240A2, NPE-180S2, NPE-210S2, NPE-240S2 condensing tankless water heaters |
Check this first
Only steps a homeowner can do safely. Do not open electrical panels or the burner area.
- Do not run the unit. Do not change settings yourself.
🛑 Stop and call a licensed pro if
- Call a licensed technician or Navien customer support (1-800-519-8794, per the manual). Do not open the unit.
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Codes for flame failure, overheating, venting or the control board that return after one reset.
- Water leaking from the heater, the relief valve discharging, or scorching around the burner area.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Safe first steps for any Navien code
- Write down the exact code shown on the controller or the number of status light flashes.
- Turn the water heater power off and back on (or press the reset button the manual describes) once. If the code comes back, stop resetting.
- Make sure the gas supply valve to the heater is open and other gas appliances in the home are working.
- Make sure the cold water supply valve is fully open and hot water taps are not partly closed.
- Look at the outside vent terminal for snow, ice, leaves or anything blocking it (look only).
Source: Navien NPE Condensing Water Heaters User's Information Manual (NPE-2, rev 201202), 5.2 Understanding Error Codes, p.18. Codes are series-specific, so your unit's own manual is the final word. Reviewed October 2026.
Ryan Giles · Red Seal Certified Plumber · Ask a plumber · Ask an HVAC technician
Related Navien codes
E003 : Ignition failureE004 : False flame detectionE012 : Flame lossE016 : Overheating of heat exchangerE030 : Exhaust overheatingE031 : Overheating of burnerE046 : Limit control abnormal operationE047 : Exhaust thermostat thermistor open or short circuitE060 : Dual venturi abnormal operationE109 : Fan motor abnormal operationE110 : Abnormal air pressureE407 : Hot water outlet thermistor open or short circuit