Code 51
Rinnai Gas Control Valve Fault

Unit displays Code 51 and will not operate

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Defective gas valve, Loose or damaged wiring to gas valve, Control board output failure, Incorrect gas type setting

How to Fix / Troubleshooting

Safety first: Turn OFF gas and power. Only qualified personnel should work directly on gas valves.

Steps to check:

  • Inspect wiring: With the front cover removed, verify that the gas valve connectors are fully seated and wiring is intact.
  • Confirm gas type: Ensure the unit is configured for the correct gas type (natural gas vs. LP) as per the rating plate and installation.
  • Reset the unit: Restore power and gas and reset. Do not repeatedly reset if Code 51 returns.

When to call a professional: A licensed gas technician must test and, if necessary, replace the gas valve assembly or control board and verify combustion.

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Repair Difficulty

Professional Required 5/5

Required Part

Gas Valve Assembly
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