Navien Error Code E773: Improper Gas Type Detected
How to Fix Navien Code E773
- Step 1: Immediately shut off the gas supply to the unit at the gas shut-off valve, usually located near the unit.
- Step 2: Open windows and doors to ventilate the area in case of a gas leak.
- 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
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
What does 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.
Affected Models
- NCB-H
- NFB-H
- NFC-H
- NHB-H
- NHW-A
- NPE-A2
- NCB
- NCB
- NCB
- NPE
- NPE
- NPE
- NHB
- NHB
- NCB
- NCB
- NPE
- NPE
- NCB
- NCB
- NPE
- NCB
- NPE
- NHB
- NCB
- NPE
- NPE
- NCB
- NCB
- NPE
- NPE
- NPE
- NPE
- NHB
- NHB
- NCB
- NCB
- NPE
- NPE
- NBP
- NPE
- NPE
- NPE
- NFC
- NFC
- NCB
- NPE
- NPE
- NPE
- NCB
- NPE
- NCB
- NPE
- NPE
- NCB
- NPE
- NHB
- NPE-S
- NPN
- NPN
- NCB
- NPE
- NCB
- NPE
- NHB
- NPB
- NFC
- NFC
- NHB
- NPF
- NPF
- NPE
- NHB
Source Documentation
| Manual | Page | Reason | Action |
|---|---|---|---|
| Navien NCB-H Installation & Operation Manual | 130 | Improper Gas Type Detected | Contact technical support at 1-800-519-8794. |
| Navien NFC-H Installation & Operation Manual | 128 | Using the wrong gas | Parameter RESET |
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Gas Valve | 30014522A | — |
| Main PCB | DEE2003 | — |
| Gas Conversion Kit | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| E001 | Ignition Failure | Warning |
| E003 | Abnormal Ignition | Warning |
| E004 | False Flame Detection | Warning |
| E012 | Flame Loss | Warning |
| E016 | Overheating | Warning |
| E030 | Exhaust Overheat Sensor | Warning |
| E031 | Inlet Thermistor Open/Short | Warning |
| E046 | Outlet Thermistor Open/Short | Warning |
| E047 | DHW Thermistor Open/Short | Warning |
| E060 | Fan Motor Abnormality | Warning |