E012
Navien Tankless Water Heater
Severity: CriticalWhat it means
Navien E012 means the flame was established and then dropped out mid-cycle — the unit lit fine, ran for a bit, and lost the burner.
The classic cause is gas pressure sagging under load: the line is undersized or another big gas appliance kicked on and starved it.
It's also caused by a marginal flame-sensing rod, partial vent blockage, or wind hitting the termination.
You get hot water that suddenly goes cold.
Affected Models
- Navien NPE-180A, NPE-210A, NPE-240A (Classic)
- Navien NPE-180S, NPE-210S, NPE-240S
- Navien NPE-2 series
- Navien NCB-E combi-boilers
- Navien NPN and NR series
Common Causes
- Gas pressure drops under load — undersized or long gas line, or a shared line with the furnace/range
- Propane tank running low (the burner dies as demand peaks)
- Flame-sensing rod dirty or weak — fine at first, loses the signal as the burner heats
- Partial vent or intake blockage choking combustion mid-run
- Strong wind across the vent termination snuffing the flame
- Condensate backing up near the burner
How to Fix It
-
Note when it happens.
Does E012 hit when the furnace, a gas dryer, or a gas range is also running? That's the tell for a gas-supply bottleneck.
Does it happen on windy days? Then look at the vent termination.
Random, all conditions? Lean toward the flame rod or venting. -
Check the propane level if you're on LP.
A tank getting low can supply enough gas to light but not enough to hold the burner at full fire.
Check the gauge — anything under about 20% is suspect.
Refill and retest before chasing anything inside the unit. -
Look at the vent and intake.
Walk outside to the termination.
Clear any nest, lint, leaves, or snow.
Check the screen isn't half-blocked.
Inside, with the breaker off, check the unit's air inlet filter and clean it. -
Clean the flame-sensing rod.
Breaker off, front cover off.
Lightly clean the flame rod tip, inspect the ceramic insulator, reseat the wire.
A weak signal that fades as the burner area heats up is a textbook E012 cause. -
Have the gas pressure tested under load.
This is the one that needs a manometer.
A tech checks inlet pressure while the unit fires at maximum and while other gas appliances run.
If it dips below spec, the gas line has to be upsized or rerun — that's the real fix, not a part swap. -
Replace the flame rod or call service.
If cleaning didn't help and gas pressure checks out, replace the flame-sensing rod.
Still dropping out after that — the control board's flame-detection circuit or the gas valve is the next suspect, which is a service call.
Frequently Asked Questions
What's the difference between E003 and E012?
E003 is ignition failure — the burner never lit at all.
E012 is flame loss — it lit, ran, then went out.
They overlap a lot on cause (gas pressure, flame rod, venting), but E012 specifically points to something that changes once the unit is running, like pressure sagging under load or wind at the vent.