Navien Error Code E777: Low water cutoff (LWCO) activated (Combi Boiler)
Navien error code E777 on a combi boiler means: Low water cutoff (LWCO) activated. It is also called Navien diagnostic code E777.
Homeowner? What Navien code E777 means for you
Call a technician Your combi boiler is reporting: Low water cutoff (LWCO) activated. The combi 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.
- If only hot water is missing, check that the hot water tap is open far enough to start the heater.
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 device has opened (low water in the system). NFC-H manual lists the reset type as: Auto reset.
Applies to: Navien fire-tube combi boilers, NFC-H series (NFC-250/200H, NFC-250/175H) and NCB-H combi boilers (NCB-250/150H, NCB-240/130H, NCB-240/110H, NCB-190/080H, NCB-190/060H)
Common causes of Navien code E777
- Low system water level
- External LWCO wiring
- LWCO fault
Navien models that use code E777
NCB-190/060HNCB-190/080HNCB-240/110HNCB-240/130HNCB-250/150HNFC-250/175HNFC-250/200H
Other Navien Combi Boiler codes
All Navien Combi Boiler error codes →
Navien code E777: homeowner questions
What does Navien code E777 mean?
Low water cutoff (LWCO) activated. The external LWCO device has opened (low water in the system). NFC-H manual lists the reset type as: Auto reset.
Is it safe to keep using my combi boiler with code E777?
It depends on the cause. The combi 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 combi boilers in Vaughan, Toronto and across the GTA. Call (647) 657-2977 or book a service call online.
Homeowner help: Tankless Water Heater No Hot Water: What to Check · Boiler Not Heating: What to Check
Troubleshooting guides
- Hot water is cold or turns cold - Navien NCB-H Navien · Combi Boiler
- Hot water not hot enough or too hot - Navien NCB-H Navien · Combi Boiler
- No space heating - Navien NCB-H Navien · Combi Boiler
- No water from hot water tap - Navien NCB-H Navien · Combi Boiler
Source: Navien NCB-H Installation & Operation Manual, 11.7 Understanding Error Codes, p.129-130; Navien NFC-H Installation Manual, 11.7 Understanding Error Codes, p.127-128. 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.