Navien Error Code E773: Improper Gas Type Detected

How to Fix Navien Code E773

1. Step 1: Immediately shut off the gas supply to the unit at the gas shut-off valve, usually located near the unit.
2. Step 2: Open windows and doors to ventilate the area in case of a gas leak.
3. Step 3: Evacuate the premises and call your local gas company or a qualified HVAC technician to inspect the unit and gas lines.

How to Reset Navien Code E773

1. Turn off the unit using the power button on the front panel.
2. Turn off the gas supply valve.
3. Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
4. Restore power at the breaker, then open the gas valve.
5. Turn the unit back on. If the error returns, the underlying issue needs repair.

Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.

What Does Navien Error Code E773 Mean?

The E773 error on your Navien tankless water heater or combi-boiler signals that the unit has detected an 'Improper Gas Type'. Navien units are designed to operate on either natural gas (NG) or propane (LP), but not both interchangeably without proper conversion. This error means the unit's control board believes it's receiving the wrong fuel. Operating with the wrong gas type can lead to incomplete combustion, producing dangerous carbon monoxide (CO), and can also damage the unit's internal components, like the burner and gas valve. This is a serious safety concern. Natural gas and propane have different densities and require different air-to-fuel ratios for proper combustion. If the unit is configured for natural gas but is receiving propane (or vice versa), it will not burn the fuel efficiently or safely. Continuing to run the unit could create a fire hazard or carbon monoxide poisoning.

Common Causes

• Incorrect gas conversion: The unit was recently converted from natural gas to propane (or vice versa), and the conversion process was not completed correctly, specifically the gas conversion switch on the main PCB.
• Gas supply issue: The gas supply to the unit is not the type it's configured for (e.g., natural gas supplied to a unit configured for propane).
• Faulty gas valve: The gas valve is malfunctioning and not regulating the gas flow correctly, leading to an improper air/fuel mixture.
• Incorrect DIP switch settings: The DIP switches on the main control board are not set correctly for the gas type being used.

Diagnostic Steps

Replacement Parts

Related Codes on Same Models

Other codes that affect the same Navien model families as E773.