Вопрос кажется простым, но если он касается работы терморегулятора, то
есть такое описание loop fault alert:


The LFA Loop Fault Alert function is used to detect any possible defects in the elements outside the controller, such as short-circuit or breaking of the sensor or actuator. The LFA function intervenes indicating a message on the display and/or deactivating the main output, if the output is at 100% and the measured temperature does not change in consequence within the integral time. This link to the integral time adapts the function to the process dynamic and is valid also with ON/OFF action. The main output deactivation is very useful in presence of a defect on the sensor or its line, as the controller could uselessly activate the output or even cause damages.
http://www.datascan.si/datasensor_katalog/ies/pdf/uk/th_e.PD...

Исходя из приведенного выше определения, перевод будет выглядеть примерно так:

Регистрация неисправности внешней цепи терморегулятора и отключение его выходного сигнала