Ruud 61 or 99 Error Code

What does Ruud 61 or 99 mean?

On Ruud RUTGH condensing tankless water heaters, error code 61 or 99 indicates a faulty inlet thermistor. The inlet thermistor measures incoming water temperature so the controller can set the firing rate; when that sensor reads abnormally or fails, the unit displays 61 or 99 and stops to avoid mis-controlling the burner.

Symptoms

• 61 or 99 shown on the remote control LED display
• Heater does not produce hot water correctly
• Inconsistent outlet temperature before the fault
• Unit faults out on startup or under demand

Common causes

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

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Diagnostic steps

1. Note the displayed code

   Record whether 61 or 99 is shown. This is a sensor fault, not a user 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 61 or 99 returns after the power cycle, the inlet thermistor likely needs professional attention.

4. Contact a dealer or qualified service technician

   The manual's solution for code 61 or 99 is to contact a dealer or qualified service technician to test and replace the inlet thermistor.

When to call a professional

Code 61 or 99 points to a failed inlet thermistor, which a dealer or qualified service technician should test and replace. Accessing and replacing the sensor involves opening the unit and working near electrical and gas components. The manual warns to make sure power is off before removing any protective cover and to refer repairs of electrical wiring and safety devices to a qualified service technician.