In exemplary embodiments, HVAC controls and corresponding error detection methods are disclosed. In an exemplary embodiment, an HVAC control generally includes an analog input configured to receive an analog signal, and an error indicator. The control is configured to receive a neutral signal at the analog input, measure a voltage of the neutral signal with respect to earth ground, to operate the error indicator to provide a first indicator status indicative of a bad ground state if the voltage is between a first voltage threshold and a second voltage threshold, and to operate the error indicator to provide a second indicator status of a reverse polarity state if the voltage is above the second threshold. The HVAC control may include at least four different indicator statuses. The HVAC control may include a comparator.