The problem could be that your upper and lower limits are set on top of each other, so the system is behaving erratically since it doesn't have any room to maneuver.
The limits should be extremely wide.
Here is an excerpt from our quick reference guide on how to access the HS and LS.
Upper and lower limit settings:
Press “SET” key and hold more than 3 seconds to enter the menu display, with “UP” or “DOWN” key adjusted to the screen, appearing “HS” or “LS” code, press the “SET” key to display the upper or lower limit set value, then press “UP” or “DOWN” key to adjust the parameters. HS means upper limit. LS means lower limit.
Factory Default = LS -44, HS +299
The system will work out of the box without adjusting any of the specialized settings such as HS or LS.
Simply reset your HS and LS set temps to factory default, and your thermostat temp to the desired level and the controller will do the rest!