Navien Error Code E777: Low water cutoff activated (Boiler)
Navien error code E777 on a boiler means: Low water cutoff activated. It is also called Navien diagnostic code E777.
Homeowner? What Navien code E777 means for you
Call a technician Your boiler is reporting: Low water cutoff activated. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Safe things you can check yourself
- Check the thermostat: right mode (Heat or Cool), set a few degrees past room temperature, and fresh batteries if it uses them.
- Make sure the unit has power: its on/off switch (often looks like a light switch near the unit) is ON and the breaker in the electrical panel is not tripped.
- Look at the pressure gauge on the boiler. If it reads much lower than usual or near zero, or water is leaking, call a technician.
- Outside, make sure the intake and exhaust pipes or vent cap are not blocked by snow, ice, leaves or a nest.
- Check that the boiler gas valve is open (handle in line with the pipe).
- Try one reset: turn the power off for 30 seconds, then back on. If the code comes back, stop resetting and call a technician.
Call (647) 657-2977Book a service call
Licensed technicians serving Vaughan, Toronto and the GTA.
What does Navien error code E777 mean?
The external LWCO input opened. Manual action: check supply water.
Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers
Common causes of Navien code E777
- Low water level at the external LWCO
- LWCO wiring or factory jumper removed without a device
- Faulty LWCO
Navien models that use code E777
NFB-175HNFB-200HNHB-055HNHB-080HNHB-110HNHB-150H
Other Navien Boiler codes
All Navien Boiler error codes →
Navien code E777: homeowner questions
What does Navien code E777 mean?
Low water cutoff activated. The external LWCO input opened. Manual action: check supply water.
Is it safe to keep using my boiler with code E777?
It depends on the cause. The boiler has locked out or cannot run properly. One reset is fine; if the code comes back, it needs a licensed technician to find the cause.
Can I reset Navien code E777 myself?
You can try one reset (power off for 30 seconds, then on). If Navien code E777 comes back, the cause is still there and a licensed technician should check it.
Who can fix Navien code E777 near me?
Aurora Star Tech Inc. repairs Navien boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Boiler Not Heating: What to Check
Troubleshooting guides
- No heat or some zones cold All brands · Boiler
- Annual service checklist - Navien NHB-H Navien · Boiler
- No space heat - Navien NHB-H / NFB-H Navien · Boiler
- Relief valve discharging - Navien NHB-H / NFB-H Navien · Boiler
Source: Navien NHB-H Installation and Operation Manual, 11.14 Understanding Error Codes, p.119; Navien NFB-H Installation Manual, 11.7 Understanding Error Codes, p.116; NHB-H User's Information Manual (V1.0 Apr 2024), 5.2, p.24. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.