Rinnai Tankless Water Heater Error Code 51: How to Fix It

Medium 30-60 minutes Medium Severity Verified June 2026
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Error Code
51
Brand
Rinnai
Product Type
water_heater
Severity
Medium
DIY Difficulty
Medium
Estimated Fix Time
30-60 minutes
Error code 51 on your Rinnai tankless water heater indicates an open circuit in the gas solenoid valve. This means the valve that controls gas flow isn't receiving proper electrical connection, so the heater shuts down for safety. Common causes include loose wiring, a failed solenoid coil, or a faulty control board.
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Tools You'll Need

How to Fix Error Code 51

  1. Turn Off Power and Gas

    Always turn off power and gas before servicing to prevent electric shock or gas leak.

  2. Access the Solenoid Valve

  3. Inspect Wiring Connections

  4. Test the Solenoid Coil

    Use caution when testing live circuits; ensure power is off.

  5. Replace the Solenoid Coil (if needed)

    Double-check gas connections for leaks after reassembly.

  6. Check the Control Board

    Control board replacement requires technical skill; improper handling can damage the unit.

  7. Restore Power and Gas

    Monitor for gas smell; if detected, turn off gas immediately and call a professional.

Parts You May Need

Gas solenoid valve coil
Check Price on Amazon
Gas solenoid valve coil
Check Price on Amazon
Gas solenoid valve coil
Check Price on Amazon
Gas solenoid valve coil
Check Price on Amazon
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When to Call a Professional

If error persists after checking wiring and replacing the solenoid coil, or if you're uncomfortable working with gas lines and electrical components, call a licensed HVAC technician or plumber. Control board replacement typically requires professional diagnosis.

Frequently Asked Questions

What does error code 51 on a Rinnai water heater mean?
Error 51 indicates an open circuit in the gas solenoid valve. The valve's electrical coil or wiring is broken, preventing the valve from opening.
Can I reset a Rinnai water heater error code 51?
You can try turning the heater off and on to reset it, but if the underlying issue isn't fixed, the code will return. Always diagnose and repair the cause first.
Is it safe to use the water heater with error 51?
No. The heater will not operate and may pose a safety risk if the gas valve malfunctions. Do not attempt to bypass the error.
How much does it cost to fix Rinnai error code 51?
DIY repair costs $20-$60 for a new solenoid coil. Professional service ranges from $150-$400, including parts and labor.
Can a dirty water filter cause error 51?
No. Error 51 is strictly an electrical issue with the gas solenoid valve. However, lack of maintenance can cause other errors.

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