Ruud 31

What does Ruud 31 mean?

On Ruud RUTGH condensing tankless water heaters, error code 31 indicates the heat exchanger is too hot. The controller senses excessive heat-exchanger temperature and stops the unit to protect it, displaying code 31. This is a hardware-protection fault that the manual routes to professional service.

Symptoms

• 31 shown on the remote control LED display
• Heater shuts down during operation
• Loss of hot water
• Repeated faulting under load

Common causes

• Heat-exchanger temperature exceeding safe limits
• Reduced water flow through the heat exchanger
• Scale buildup impairing heat transfer

Diagnostic steps

1. 01

   Turn off faucets and let the unit cool

   Turn off all hot water faucets so the heat exchanger can cool before restarting.

2. 02

   Power-cycle the heater

   Turn off the heater, unplug it for about 30 seconds, plug it back in, restart, then turn on a hot water faucet and recheck the display.

3. 03

   Record the code if it persists

   If 31 remains, note the displayed code for the technician.

4. 04

   Contact a dealer or qualified service technician

   The manual's solution for code 31 is to contact a dealer or qualified service technician to diagnose the heat-exchanger condition.

When to call a professional

Code 31 is a heat-exchanger over-temperature fault best handled by a dealer or qualified service technician, especially if it returns after a power cycle. Diagnosing flow restriction or heat-exchanger condition on a sealed condensing unit requires specialized tools. The manual directs repairs of burners and safety devices to a qualified service technician and warns against attempting them yourself.