The blue LED illuminates when the controller isn’t reading one of the temperature sensors. This is more common during initial installation when the installer hasn’t yet configured the temperature sensors. The default configuration for the temperature source is 1 4 4. OAT = 1 (the electronic sensor), FRONT = 4 (the OEM thermistor plugged into touchscreen), and REAR = 4 (the OEM thermistor plugged into touchscreen)
If the OEM sensors are plugged into the 4 pin connector on the controller board (early versions of the Waiter ECC) then the configuration would be 1 0 0 . (0 says the OEM sensors are plugged into the contole board instead of the touchscreen.
If electronic sensors are used for the internal temperature sensors, then the addresses will need to be determined by trial and error. See the TECHNICAL MANUAL for how to determine the addresses.
If the configuration is correct yet the blue LED is lite, the faulty sensor should be displaying a “-99” on the temperature readout.