An example HVAC system includes a furnace including a gas valve, a circulator motor to circulate air through the HVAC system, and a current sensor configured to detect a current supplied to the circulator motor. The system also includes a controller configured to disable the gas valve when a detected current supplied to the circulator motor is outside of a specified operating current range. A detected current to the circulator motor outside of the specified operating current range is indicative of a malfunction of the circulator motor. Example methods of operating a gas valve in an HVAC system are also disclosed.