The short answer
When a Navien tankless water heater has a problem, it shows a code like E003 on the front panel. The code tells you what the unit detected. Write the code down exactly, try the reset button once, and if the code comes back, call us.
Common Navien error codes
| Code | What it means | What it usually points to |
|---|---|---|
| E003 | Ignition failure | The unit could not light. First make sure the gas supply valve to the heater is open. |
| E004 | False flame detection | The unit sees a flame signal when it should not. Often an electrical grounding issue. |
| E012 | Flame loss | The burner lit, then lost the flame. A dirty intake air filter or a grounding issue are common causes. |
| E016 | Heat exchanger overheating | Usually scale buildup or a clogged cold water inlet filter. The heat exchanger often needs to be flushed. |
| E030 | Exhaust overheating | The unit shut down because the flue got too hot (over 149 °F). Like E016, it often points to scale or a clogged inlet filter. |
| E046 | Limit control fault | A safety limit device tripped. This one needs a technician. |
| E109 | Fan motor fault | The combustion fan is not running right. A dirty intake air filter is a common cause. |
| E110 | Abnormal air pressure | Something is restricting air. Check that the outdoor exhaust pipe is not blocked. |
| E407 | Hot water outlet sensor | The outlet temperature sensor is open or shorted. This one needs a technician. |
Code meanings come from Navien's NPE-2 owner and installation manuals. Other Navien models use some different codes, so check the manual for your model or give us a call.
What you can safely check yourself
- Write the code down exactly. E003 and E030 point to very different problems.
- Make sure the power is on and the gas valve to the heater is open.
- Press the reset button on the front panel one time.
- Look outside: make sure the exhaust and intake pipes are not blocked by leaves, snow or a nest.
If you smell gas, do not reset anything. Leave the house and call the gas company from outside.
When to call a plumber
Call us if the same code keeps coming back after a reset, if the unit is leaking, or if the code is one the manual says needs a technician. Clearing a code does not fix what caused it. Codes like E016 and E030 often mean the heat exchanger needs to be flushed, which is part of yearly tankless maintenance.
Tankless service with Acts of Service Plumbing
We install and service Navien tankless water heaters across Tulsa and nearby cities. A service call starts at $89 and is waived when you approve the repair, and you get a flat-rate, upfront price before any work starts. Navien tankless installed starts at $5,999. See tankless water heaters or read a real tankless maintenance job story.
Page last updated October 2026.
Straight Answers
What does E003 mean on a Navien water heater?
E003 means ignition failure: the unit could not light. First make sure the gas supply valve to the heater is open, then press reset once. If it comes back, call a plumber.
What does E016 mean on a Navien?
E016 means the heat exchanger is overheating. It is often caused by scale buildup or a clogged cold water inlet filter, and the heat exchanger usually needs to be flushed.
Can I just reset my Navien when it shows a code?
You can press reset once. If the same code comes back, the cause is still there and the unit needs to be checked.
How often does a tankless water heater need maintenance?
We recommend yearly maintenance. On one Broken Arrow maintenance visit we also found and fixed a small condensate line leak.
