Thermostat displays E9 and may indicate 'Internal memory error' or 'Configuration fault'; settings may reset unexpectedly.

Safety note: This is an internal thermostat issue; wiring changes are usually not required.

Steps:

• Soft reset: Use the thermostat menu to perform a soft reset or restart. Do not cut power during this process.
• Factory reset: Back up any custom schedules in the Rheem app, then perform a factory reset from the thermostat settings. Reconfigure system type and preferences following the installation guide.
• Firmware update: Connect the thermostat to Wi-Fi and check for firmware updates via the Rheem app. Apply any available updates and allow the thermostat to reboot fully.
• Monitor operation: If E9 does not return after reset and update, continue normal use.
• If E9 recurs frequently: The internal memory is likely failing. Replacement of the thermostat is recommended; contact Rheem or a professional installer.