Navien E012 Error Code: Flame Loss During Operation

What you'll notice with E012

• Hot water starts fine, then goes cold mid-shower
• Worse when the furnace, range, or dryer runs at the same time
• Unit relights repeatedly and eventually locks out

What causes it

Gas pressure drop with other appliances running, dirty burner, or exhaust restriction.

Safe steps you can take right now

1. 1Note whether it happens only when another gas appliance is running — that's a strong clue.
2. 2Clean or check the air intake filter if your unit is in a dusty garage.
3. 3One power cycle is fine; if it recurs, schedule service.

How we fix E012

Flame loss almost always traces to dynamic gas pressure sagging under combined load, a fouled burner, or an exhaust restriction. We test pressure with everything running, clean the burner assembly, and verify vent length and slope against Navien's spec.

Measure dynamic gas pressure, clean the burner and air intake filter, and clear vent restrictions.