On the covered Navien tankless water heater, E003 means ignition failure. First, check that the main gas supply valve to the heater is open. Then: Navien's self-diagnostic list: the main gas supply valve is open, gas pressure is within the operating range, the gas system and orifice are right, the dual venturi operates properly, the dipswitch settings are right, and the ground connection screws on the heat exchanger are tight. Gas-system checks are for a licensed professional.
Differential
Likely causes of “Navien tankless water heater code E003”, and how to tell them apart
- 1
The main gas supply valve is closed
What separates it The burner never lights
How to confirm Open the gas valve
- 2
Gas pressure outside the operating range
What separates it Weak or no flame
How to confirm Technician checks the pressure
- 3
The wrong orifice or gas system
What separates it A mismatch of gas type
How to confirm Technician checks
- 4
A dual venturi fault
What separates it The mix is wrong
How to confirm Technician checks
- 5
Loose ground screws on the heat exchanger
What separates it Poor sensing
How to confirm Technician tightens them
Before you touch a setting
Record this first — changing settings destroys the evidence
- Whether the gas valve is open
- Whether other gas appliances work
Try in this order
0 of 4 completedWhat to do first
ReversibleCheck that the main gas supply valve to the heater is open.
Correct only the documented fault domain
ReversibleNavien's self-diagnostic list: the main gas supply valve is open, gas pressure is within the operating range, the gas system and orifice are right, the dual venturi operates properly, the dipswitch settings are right, and the ground connection screws on the heat exchanger are tight. Gas-system checks are for a licensed professional.
Check the gas valve
ReversibleIs it open?
Call a licensed professional
ReversibleFor the gas checks.
Model-specific
What is true of this model and not of its siblings
- Ignition failure
- The heater tries to light the burner a set number of times. If no flame is detected, it stops and shows E003.
- Navien's list
- The main gas valve is open, gas pressure is within range, the gas system and orifice are right, the dual venturi works, the dipswitch settings are right and the ground screws on the heat exchanger are tight.
- What an owner does
- Only the gas valve check is for an owner; everything else is for a licensed professional.
- What ignition failure covers
- The heater tries to light a set number of times. If it never proves a flame, it stops and shows E003. The reason may be gas, air, the igniter or the sensing, so the list Navien gives is long.
- An owner's first check
- The only part of the list an owner should handle is the main gas valve, which should be fully open, with the handle in line with the pipe. Check that other gas appliances, such as the stove, light normally.
- Why the rest is professional work
- Gas pressure, orifices and venturi settings need instruments and training. A wrong setting can create a hazard, so leave them to a licensed professional.
- What the display tells you next
- If E003 appears only on the first demand after a long gap, air in the gas line may be the cause, and a second attempt may light the heater. If it appears on every attempt, the cause is persistent and needs a technician. Note which pattern you have.
Stop boundary
When this stops being a self-service repair
- !Navien's self-diagnostic list includes gas pressure, orifice and venturi, which are for a licensed professional
- !Check only that the gas valve is open
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does E003 mean on a Navien tankless water heater?+
Ignition failure.
What is the first check?+
The main gas supply valve.
Can I check gas pressure?+
No, a professional must.