No hot water at all
A hot tap opens, the unit tries to start, then the display shows E012 and water stays cool.
Start here: Start with gas supply and a basic reset, then check the intake and exhaust outside.
Tankless water heater error code
Navien Tankless Water Heater Code E012
Direct answer: Navien code E012 usually means the burner tried to light but lost flame or could not keep a stable burn. The first things to check are whether the gas supply is fully on, the unit has been recently interrupted by wind or vent blockage, and whether the air intake or condensate drain is restricted.
Most likely: Most often, this shows up after a gas interruption, a partially closed gas valve, a blocked intake or exhaust, or condensate backing up into the unit.
Treat E012 like a failed fire-up, not a random electronics glitch. If the unit clicks, tries to ignite, then drops out and shows the code again, work the easy airflow and supply checks first. Reality check: one windy day, one closed gas valve after other work, or one plugged condensate line can be enough to trigger this. Common wrong move: resetting it over and over without checking the vent and gas shutoff first.
Don’t start with: Do not start by ordering a control board or opening the gas train. On this code, the simple outside checks are far more common than a failed internal gas component.
If you smell gas or hear rough ignitionStop using the water heater, leave the area if needed, and call the gas utility or a qualified service tech.
If the code appeared right after plumbing, gas, or vent workCheck for a shutoff left partly closed, a disconnected vent section, or a condensate line knocked loose.
Last reviewed: 2026-04-17
What code E012 usually looks like in the house
Hot water for a few seconds, then cold
The burner seems to catch briefly, but the unit drops out and throws the code once flow continues.
Start here: Look for vent restriction, condensate backup, or unstable gas supply before assuming an internal part failed.
Code appears only in bad weather
The heater works on calm days but faults during wind, heavy rain, or freezing conditions.
Start here: Inspect the vent termination and intake for wind-driven blockage, ice, debris, or sagging vent sections holding water.
Code started after other work in the house
The error began after gas work, plumbing work, remodeling, or moving stored items near the unit.
Start here: Check that the gas shutoff is fully open, the intake area is clear, and the condensate tubing was not bumped or pinched.
Most likely causes
1. Gas supply interruption or low gas flow to the water heater
E012 commonly shows up when the burner lights poorly or loses flame because the unit is not getting steady gas.
Quick check: Make sure the water heater gas shutoff is fully parallel with the pipe and confirm other gas appliances are working normally.
2. Blocked or disturbed intake or exhaust venting
A tankless unit needs clean airflow to light and stay lit. Leaves, nests, ice, or a loose vent joint can upset combustion quickly.
Quick check: Inspect the vent termination outside and the area around the unit for blockage, sagging pipe, or anything covering the intake.
3. Condensate drain restriction on a condensing tankless water heater
If condensate cannot drain, water can back up and interfere with normal burner operation or trip safety logic during ignition.
Quick check: Look for water in the cabinet base, a kinked condensate tube, or a trap and drain line that are dirty or plugged.
4. Ignition or flame-sensing trouble inside the burner section
If supply and venting look normal but the unit repeatedly clicks, lights weakly, or drops flame, the igniter or flame rod may be fouled or worn.
Quick check: Listen for repeated ignition attempts and watch whether the unit ever catches flame briefly before locking out again.
Step-by-step fix
Step 1: Confirm it is really an E012 ignition-flame problem
Tankless units can throw similar-looking no-heat complaints for very different reasons. You want to make sure you are chasing a fire-up problem, not a flow or temperature setting issue.
- Open one hot water fixture fully and watch the display at the unit if you can do it safely.
- Confirm the code shown is E012, not a different code that appeared earlier or after repeated resets.
- Note whether the unit clicks or tries to ignite before the code appears, or whether it faults immediately.
- Check that the unit has power and the front panel is not showing an unrelated standby or power issue.
Next move: If you clearly see E012 after an ignition attempt, continue with supply and vent checks. If there is no ignition attempt, no code, or a different code appears, stop chasing E012 and troubleshoot the actual displayed problem.
What to conclude: A true E012 points you toward gas, air, condensate, or burner ignition stability rather than a simple temperature setting problem.
Stop if:
- You smell gas anywhere near the unit.
- The cabinet is hot, scorched, or making harsh booming ignition sounds.
- Water is leaking into electrical areas of the unit.
Step 2: Check the easy gas-supply items first
A partly closed gas valve or recent gas interruption is one of the most common real-world causes, and it is the least invasive thing to rule out.
- Find the gas shutoff serving the water heater and make sure the handle is fully open, parallel with the gas pipe.
- If any recent work was done nearby, verify no one left a service valve partly closed.
- See whether other gas appliances in the home are operating normally.
- If the gas supply was recently interrupted, turn the unit off and back on once to retry after supply is restored.
Next move: If the heater runs normally after restoring full gas flow and one reset, the problem was likely supply-related. If other gas appliances also struggle, or the water heater still drops into E012, move on to venting and condensate checks.
What to conclude: Good gas flow to the house but repeated E012 at the heater makes airflow, condensate, or internal ignition trouble more likely.
Step 3: Inspect the intake and exhaust path for blockage or weather trouble
These units are sensitive to restricted airflow. Outside terminations, screens, elbows, and low spots in venting are common places for trouble.
- Go outside and inspect the vent termination and intake opening for leaves, lint, nests, ice, snow, or wind-blown debris.
- Clear only loose visible debris by hand. Do not disassemble vent piping or poke deep into the vent run.
- Look for signs of water staining, sagging vent sections, or a vent joint that has slipped apart.
- Inside, make sure stored items, insulation, or laundry supplies are not crowding the unit air openings.
Next move: If you clear a blockage and the unit lights normally, monitor it through several hot-water calls. If the vent path looks clear and the code returns, check the condensate drain next.
Step 4: Check for condensate backup and obvious water-related blockage
On condensing tankless units, a dirty trap or kinked condensate line can cause nuisance flame and ignition faults that look electrical at first.
- Look under and around the unit for standing water, drips, or a condensate tube that is kinked, pinched, or pulled loose.
- If the drain line is accessible, make sure it is not frozen, crushed, or submerged at the end.
- If the trap or drain tubing is visibly dirty and the manual procedure is familiar to you, clean only the homeowner-serviceable condensate path.
- Restore power and test one hot-water call after the drain path is open again.
Next move: If the unit runs after the condensate path is cleared, keep an eye on it for the next day or two for repeat backup. If gas, venting, and condensate all check out but E012 keeps returning, the remaining likely causes are inside the burner section and should be serviced professionally.
Step 5: Reset once, test, then move to burner service instead of guessing at parts
After the common external causes are ruled out, repeated resets do not fix the root problem. At that point the likely work involves combustion testing, cleaning, or internal gas and ignition components.
- Turn the unit off and back on once after completing the checks above.
- Run hot water at one fixture and listen for a clean ignition versus repeated clicking and dropout.
- If E012 returns again, schedule qualified service and report exactly what you found: gas supply status, vent condition, condensate condition, and whether the flame ever catches briefly.
- Until it is repaired, avoid relying on repeated resets to force operation.
A good result: If the unit now lights cleanly and stays running through several calls, keep using it but recheck the vent and condensate path after the next storm or cold snap.
If not: If the code comes back after one proper reset, stop there and have the burner and flame-sensing system serviced.
What to conclude: At this point the likely repair is not a safe guess-and-buy homeowner part. It needs combustion-side diagnosis with the right tools.
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FAQ
What does Navien code E012 usually mean?
It usually means the unit failed to establish or hold a stable flame during ignition. In plain terms, the heater tried to fire but something in the gas, air, condensate, or burner side kept it from staying lit.
Can I just reset the water heater and keep using it?
One reset after checking the obvious items is reasonable. Repeated resets are not a fix. If E012 keeps coming back, the unit still has an ignition or flame-stability problem and needs more than a reboot.
Can wind or cold weather cause E012?
Yes. Strong wind, ice, snow, or wind-blown debris at the vent termination can upset combustion enough to trigger this code. That is why the outside vent and intake check is worth doing early.
Is E012 usually a bad control board?
No. External causes like gas interruption, vent blockage, or condensate backup are more common. Control and gas-train parts are not good first guesses on this code.
Should I clean the flame sensor or igniter myself?
Not as a casual first move. Once you are past the gas, vent, and condensate checks, the remaining work is in the combustion section and is better handled by a qualified tech, especially on a gas-fired tankless unit.
What should I tell the service tech to save time?
Tell them whether other gas appliances are working, whether the water heater clicks or briefly lights, whether the vent termination was clear, and whether you found any condensate backup or water under the unit. That gives them a much better starting point.