Navien E773: Wrong Gas Type Detected
On this page (5 sections)
The Short Answer: In Navien’s NPE-2 manual, E773 means using the wrong gas: the heater’s combustion readings don’t match the gas type it’s set up for, such as natural gas versus propane. Navien’s only listed action is to contact technical support. Don’t keep resetting it, and don’t change DIP switches or settings yourself. Confirm which gas your home uses and what the rating plate says, then call your installer or Navien.
What E773 means
Navien’s NPE-2 manual lists:
| Code | Navien’s description | Navien’s listed action |
|---|---|---|
| E773 | Using the wrong gas | Contact Technical Support |
| E788 | Discrepancy between the gas type on the panel DIP switch setting and the panel | Check the supplied gas type and match the gas type setting on the DIP switch and the panel |
Some displays add a two-digit sub-code, which is why you may see 773-00. The sub-code can help Navien narrow the cause, so include it when you call.
These definitions come from the NPE-2 (NPE-A2 and NPE-S2) user’s manual. If you have a different Navien series, check its manual. Codes aren’t always shared across product lines.
Why it happens
- New installation set up for the wrong gas. Navien tankless units can be configured for natural gas or propane. If the setting doesn’t match the supply, the control may detect abnormal combustion.
- Recent move or reused heater. A unit moved from a propane home to a natural gas home, or the reverse, must be converted by a qualified installer.
- Incomplete conversion. A conversion where the settings were changed but other required steps weren’t completed, or the reverse.
- A control board or display was replaced and the gas type setting wasn’t re-entered.
- Gas supply problems. Very low or unstable gas pressure, or a propane supply problem, can produce combustion readings that don’t look right to the control.
What you can check
- Photograph the code, including any sub-code.
- Find out which gas you have. A utility meter and bill mean natural gas; a tank and supplier mean propane.
- Read the rating plate on the side of the heater for the gas type it was built or labeled for, and look for a conversion label.
- Think about recent changes: a new install, a move, a board replacement, a conversion, or new gas piping.
- Leave the heater off and contact your installer or Navien technical support (1-800-519-8794 in the NPE-2 manual) with the model, serial number and code.
Resetting won’t fix a gas mismatch, and running the heater until the code appears again doesn’t help diagnose it.
What the technician will check
A qualified gas technician will compare the heater’s gas type setting with the supply, confirm whether a conversion was done correctly with Navien’s procedure, and measure inlet gas pressure. They then use a combustion analyzer to make sure the burner is burning cleanly. Navien’s conversion procedure is for qualified installers. It is not an owner adjustment.
Frequently Asked Questions
Q: E773 appeared on a heater that has worked for years. How can the gas be wrong now? A: If nothing changed with your gas or the heater, the code may be reacting to a gas supply problem, such as low propane, a failing regulator or a utility pressure issue, or to a fault in the heater’s sensing. A technician needs to check the gas pressure and combustion.
Q: Can I fix E773 by flipping the gas DIP switch? A: No. Changing the gas type involves more than a switch setting and must be done by a qualified installer using Navien’s procedure. A wrong setting can cause poor combustion and carbon monoxide.
Manuals and supporting references
These links distinguish general safety information from model-specific documentation. A manual directory helps you locate your unit’s instructions; it does not establish that every model uses the same parts, codes, or test values.
- Navien NPE-2 Series user's information manual (opens in a new tab)Navien NPE-A2 and NPE-S2 error table: E773 (using the wrong gas) and E788 (gas type setting discrepancy).
- Navien: manuals and product documents (opens in a new tab)Model-specific owner information; service manuals are intended for qualified professionals.
- PG&E: recognizing and responding to a gas leak (opens in a new tab)Emergency actions for suspected fuel-gas leaks.
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