E004 False flame detected

What the control is telling you

The control sees a flame signal when there should be no flame. Manual action: check the electrical ground.

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

Likely causes

• Poor or missing electrical ground
• Contaminated, wet or shorted flame rod
• Gas valve not closing fully (flame present after shutdown)

Test and repair steps

1. Verify the boiler is plugged into a properly grounded outlet, or if hard-wired that ground is not taken from gas or water piping.
2. Check the ignition ground wire at the casing and test ground continuity with a meter.
3. Check polarity of the power supply connection.
4. Read the Flame Value in Status Info 70 or less means flame on, 175 or more means flame off. A low value with the burner off confirms a false signal.
5. Warning: Power off. Inspect and clean the flame rod and its wire; replace if damaged.
6. Warning: If flame stays on after the call ends, shut the manual gas valve and replace the gas valve.

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
• E012 Flame loss
• E016 Heat exchanger overheat (check flow / system filters)
• E030 Exhaust overheat
• E031 Burner overheat
• E046 Heat exchanger thermistor fault
• E047 Exhaust thermistor fault