An HVAC controller, a method for determining the source of a reset of a HVAC unit and a HVAC system are disclosed herein. In one embodiment, the HVAC controller includes: (1) a power on reset (POR) register configured to indicate if a POR has occurred for said controller, (2) a non-volatile memory having a first reset code section and a second reset code section, wherein said first and second reset code sections are each configured to store a reset code and (3) a processor configured to deduce when a source of a reset for said controller is a watchdog reset based on content of said POR register, said first reset code section and said second reset code section.