- Boilers
- Tankless gas water heater
E003
Navien E003 on a tankless water heater: ignition failure
Risk level
High
Professional inspection is recommended.
Urgency
High
Quick answer
The heater could not light the burner. Navien's first action is to make sure the main gas supply valve is open. Then reset once with the Back button; if E003 returns, call an authorized technician or Navien technical support.
Safety first
Stop and check this first
- If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
- Do not remove the front cover to look inside: Navien warns that operating the heater with the front cover open can cause fire or carbon monoxide poisoning, and that the cover may only come off with the power disconnected.
Safe checks you can perform
- Main gas supply valve open
- One reset with the Back button
- Possible freezing
- Diagnosis by a licensed professional
Leave these tasks to a qualified professional
- Do not attempt this professional task: Inspect ignition and combustion
- Do not attempt this professional task: Measure inlet gas pressure at maximum firing
- Do not attempt this professional task: Confirm gas type and setting
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Inspect ignition and combustion
What they doIf supply is correct, the professional inspects ignition parts and venting and checks the gas and air ratio with a combustion analyzer as the manual describes.
They must show youcombustion readings and successful ignitions after the repair.
In writingpart replaced and why.
Measure inlet gas pressure at maximum firing
What they doWith a manometer on the heater's pressure port, the professional ramps the heater to maximum firing rate with several fixtures open and reads inlet pressure against the range in the installation manual.
They must show youthe reading at maximum firing.
In writingmeasured pressure against the manual's range.
Confirm gas type and setting
What they doThe professional checks that the rating plate matches the gas supplied and that DIP switch 1 on the front panel matches the gas type.
They must show youthe rating plate and DIP switch setting.
In writinggas type confirmed.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Main gas supply valve open
- Who:
- you.
- How:
- look at the gas valve on the gas line to the heater; Navien's manual shows its opened and closed positions.
- Result that matters:
- whether the valve is open.
- If it was closed and you do not smell gas:
- open it and reset with the Back button.
- If it was open:
- continue with the next check.
- Evidence to keep:
- photo of the valve position.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
One reset with the Back button
- Who:
- you.
- How:
- press the Back button on the front panel. Navien's manual says resetting may solve the problem when an error appears.
- Result that matters:
- whether E003 comes back.
- If the heater runs normally:
- note the date; if E003 returns later, mention that it was reset before.
- If E003 returns:
- do not keep resetting; Navien says to contact an authorized technician, a licensed professional or its technical support.
- Evidence to keep:
- photo of the code before and after the reset.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
Possible freezing
- Who:
- you.
- How:
- think about whether there was freezing weather and whether hot water stopped flowing. Navien links E003 and E110 to a frozen unit.
- Result that matters:
- whether freezing is plausible.
- If it is:
- press the Power button to turn the heater off, close the gas valve and open the hot water faucet closest to the heater, as Navien describes, and call a technician to thaw and check for leaks.
- If there was no frost:
- the gas or ignition branch is more likely.
- Evidence to keep:
- date and outdoor temperature.
Navien's thaw procedure continues by heating the heat exchangers. Leave that step to a technician if it means opening the unit.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual · Navien preventing a frozen tankless water heater
Diagnosis by a licensed professional
- Who:
- an authorized technician or licensed gas professional.
- How:
- measures inlet gas pressure, checks gas type against the rating plate and the gas type DIP switch, and inspects ignition and venting.
- Result that matters:
- the cause confirmed by measurement.
- If pressure or gas type is wrong:
- the supply is corrected before touching parts.
- If supply is correct:
- ignition and flame detection parts are tested.
- Evidence to keep:
- written report with readings.
Navien says measuring inlet gas pressure should be performed by a licensed professional only.
Evidence: Navien NPE-A2 and NPE-S2 installation and operation manual
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Boilers
- Brand
- Navien
- Product type
- Tankless gas water heater
Known code variants
- calentador Navien E003
- Navien 003
- Navien E003
- Navien E003 fallo de encendido
- Navien E003 ignition failure
- Navien error E003
What it means
Navien defines E003 as ignition failure and gives one owner action: ensure the main gas supply valve is open. Behind the code are the gas supply, the ignition and flame detection parts and the conditions for safe combustion; Navien also lists E003 among the codes a frozen unit can store. Inlet gas pressure must be measured by a licensed professional. The code alone does not prove an igniter, gas valve or board failed.
Warnings and stop conditions
- Criticalsource verified
If you smell gas: do not try to light any appliance, do not touch any electrical switch and do not use any phone in the building. Call your gas supplier from a neighbor's phone and follow its instructions; if you cannot reach it, call the fire department.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
- Highsource verified
Do not remove the front cover to look inside: Navien warns that operating the heater with the front cover open can cause fire or carbon monoxide poisoning, and that the cover may only come off with the power disconnected.
Evidence: Navien NPE-A2 and NPE-S2 installation and operation manual
Symptoms and causes
Probable causes · in order
- Main gas supply valve closed or no gasPossible
Navien's only owner action for E003. Fits after gas work, a meter change or a closed valve.
Evidence: Navien NPE-A2 and NPE-S2 user's information manual
- Unit frozenPossible
Navien says a frozen unit can show ignition failure (E003). Fits after freezing weather, especially if no hot water flows.
Evidence: Navien preventing a frozen tankless water heater
- Gas pressure, gas type or ignition faultPossible
Inlet pressure out of range, gas type not matching the unit or a fault in ignition parts. Only a licensed professional can measure these.
Evidence: Navien NPE-A2 and NPE-S2 installation and operation manual
Virtual technician
Does E003 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Navien NPE-A2 and NPE-S2 user's information manual
Navien · 2020 · manual
- 2
Navien NPE-A2 and NPE-S2 installation and operation manual
Navien · 2026 · manual
- 3
Navien preventing a frozen tankless water heater
Navien · 2024 · official_doc
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