Ruud 65 Error Code

What does Ruud 65 mean?

On Ruud RUTGH condensing tankless water heaters, error code 65 indicates a faulty outlet thermistor. The outlet thermistor measures the temperature of the water leaving the unit so the controller can hold the set point; when that sensor fails or reads abnormally, the heater displays code 65 and shuts down to avoid delivering uncontrolled-temperature water.

Symptoms

• 65 shown on the remote control LED display
• Outlet water temperature not holding the set point
• Heater shuts down during operation
• Loss of hot water

Common causes

• Faulty outlet (outgoing water) thermistor
• Damaged or shorted thermistor wiring/connection
• Sensor reading out of range

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Diagnostic steps

1. Note the code

   Record that 65 is displayed; this is a sensor fault rather than a homeowner setting.

2. Power-cycle the heater

   Turn off the faucets, turn off the heater, unplug it for about 30 seconds, plug it back in, restart, then recheck the display.

3. Confirm the code persists

   If 65 returns after the power cycle, the outlet thermistor likely needs professional service.

4. Contact a dealer or qualified service technician

   The manual's solution for code 65 is to contact a dealer or qualified service technician to test and replace the outlet thermistor.

When to call a professional

Call a dealer or qualified service technician for code 65. A failed outlet thermistor can cause uncontrolled water temperatures, and the manual warns that water above 125F can cause severe burns or death. Replacing the sensor requires opening the unit and working near electrical components; the manual directs such repairs to a qualified professional and to ensure power is off before removing covers.