This section describes troubleshooting for the thermostat.
An error code indicates that technical assistance may be required.
Try cycling the power to the thermostat as a first method to clear the error. See
Table 12, p. 47
Note: On the display, error codes appear at the bottom of the display.
Note: On the programmable thermostat, the error code alternates with the time on the display.
Table 10. Error Codes
System Test Mode
You can run diagnostic tests on the thermostat to verify that the thermostat is functioning properly
and that the devices in the system are wired properly.
To enter system test mode:
1. Apply electrical power to the thermostat.
2. Enter installer configuration mode:
for additional information.
Thermistor Error; occurs when the configured thermistor reading is out of range (less
than 14°F (-9.9°C) or greater than 122°F (50°C). If this error occurs:
• All Heat/Cool outputs turn off.
• If the fan mode is Auto, the thermostat turns off the fan.
• If the fan mode is On, the thermostat leaves the fan on.
Permanent data error. Access error or checksum error is detected.
Input voltage out of range - too low or too high. Input voltage is lower than 18Vac or
higher than 34Vac. The error code display will remain on for 30 sec after the detection
of out of range input voltage.
RTC Error (this error can only appear on the programmable thermostat).
Memory error (write and read 0x55 and 0xAA failed). Only checked during power up test.