Navien Tankless Water Heater Error Code 304: How to Fix It
Medium 30-60 minutes Medium Severity
Verified June 2026
- Error Code
- 304
- Brand
- Navien
- Product Type
- water_heater
- Severity
- Medium
- DIY Difficulty
- Medium
- Estimated Fix Time
- 30-60 minutes
Ad
Tools You'll Need
- Multimeter with ohms and AC voltage settings
- Screwdriver set (Phillips and flathead)
- Owner's manual for your specific Navien model
How to Fix Error Code 304
-
Power Off and Restart
Make sure to disconnect power to avoid electric shock. -
Check Gas Supply
Do not use any open flame or create sparks while checking gas lines. -
Inspect Wiring to Gas Valve 2
Disconnect power before opening the unit. Capacitors may retain charge – allow time to discharge. -
Measure Gas Valve Resistance
-
Test Voltage to Gas Valve
Exercise caution when working with live voltage. Use insulated tools. -
Replace Gas Valve 2 if Needed
Gas valve replacement may require purging air from gas line. Consider professional help.
Parts You May Need
Gas valve assembly (compatible with Navien model)
Check Price on Amazon
Gas valve assembly (compatible with Navien model)
Check Price on Amazon
Gas valve assembly (compatible with Navien model)
Check Price on Amazon
Gas valve assembly (compatible with Navien model)
Check Price on Amazon
Ad
When to Call a Professional
If you are uncomfortable working with gas or electrical components, or if after following these steps the error persists, contact a licensed plumber or HVAC technician. Gas valve replacement involves handling natural gas and may require special tools and expertise.Frequently Asked Questions
Can I reset Navien error code 304?
Yes, try a full power cycle. Turn off the unit at the breaker for 30 seconds, then turn it back on. If the error returns, further troubleshooting is needed.
What does gas valve 2 fault mean?
It means the control board detected an electrical or mechanical problem with the second gas valve, which controls gas flow during operation. This can be due to wiring issues, a faulty valve coil, or a bad control board.
How much does it cost to fix Navien error 304?
If you DIY, a replacement gas valve costs around $50-$150. Professional repair (including labor) typically ranges from $200-$500.
Is it safe to use the water heater with error 304?
No. The unit will not operate safely, as the gas valve fault can prevent proper combustion. Do not attempt to bypass the error.
Do I need to call a technician for error 304?
Not necessarily. Basic checks like power cycle, gas supply, and wiring inspection can be done by a homeowner. If you need to replace the gas valve or test the control board, professional help is recommended.