E9
Ruud EEPROM / Control Board Memory Error

Tankless water heater shows E9 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

Corrupted firmware on main PCB, Power surge damage, Incompatible replacement control board, Internal control board failure

How to Fix / Troubleshooting

Safety first: Turn OFF power at the breaker before touching any internal components.

  • Step 1 – Power cycle: Turn the unit OFF, switch the breaker OFF for at least 5 minutes, then restore power. Attempt operation again.
  • Step 2 – Check for moisture or corrosion: Remove the front cover and inspect the control board for signs of water intrusion, corrosion, or burnt components. Address any leaks before replacing electronics.
  • Step 3 – Verify correct board: If the board was recently replaced, confirm the part number matches the Ruud model and that any required programming was performed.
  • Step 4 – Replace control board: Label all connectors, disconnect wiring, remove mounting screws, and install a new OEM Ruud main control board. Reconnect harnesses exactly as before.

Because EEPROM and firmware issues are internal to the board, repair is not practical; replacement is the standard fix. If E9 persists after replacement, contact Ruud technical support.

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Repair Difficulty

Hard 4/5

Required Part

Main Control Board (PCB)
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