E012 Flame loss

What the control is telling you

The flame went out during operation. Manual action: check gas, venting and the condensate trap.

Applies to: Navien NHB-H (NHB-055H/080H/110H/150H) and NFB-H fire-tube (NFB-175H/200H) condensing boilers

Likely causes

• Low or unstable gas pressure
• Blocked or over-length vent / intake
• Condensate trap empty, blocked or backing up
• Dirty flame rod
• Wrong orifice or combustion setting

Test and repair steps

1. Check inlet gas pressure at maximum fire NG 3.5-10.5 in WC, LP 8.0-13.0 in WC.
2. Inspect the exhaust and intake for blockage, snow, separated joints, and verify length/elbows are within limits (2 in: 65 ft, 3 in: 150 ft; 90° = 8 ft / 5 ft).
3. Check the condensate line slopes down at least 1/4 in per ft, is not frozen, and the trap is filled with water.
4. Clean the flame rod and check the Flame Loss count in Service Status Info.
5. Check the air intake filter for lint/dust.
6. Verify CO2 at low and high fire against the combustion table; at high fire never adjust the valve - check the orifice instead.

Settings for these units

Installation clearances (indoor) · Navien NHB-H

Bracket gives 5/8 in (16 mm) from the wall; studs at 16 in on centre.

Common vent installs: 36 in above the top and 24 in in front are recommended for service.

Installation clearances (indoor) · Navien NFB-H

Do not install on carpet; indoors only.

Remove the wood pallet and refit the 6 screws to keep the cabinet airtight.

Models that show this code

6 models in Navien NHB-H, Navien NFB-H

Other codes on the same units

• E001 Heat exchanger overheat
• E003 Ignition failure
• E004 False flame detected
• E016 Heat exchanger overheat (check flow / system filters)
• E030 Exhaust overheat
• E031 Burner overheat
• E046 Heat exchanger thermistor fault
• E047 Exhaust thermistor fault