My SmarTracker seems to keep heating after the water reaches the set point.

A relay may have gone bad, to check this you will need to remove the rear panel by powering down the unit, unplug the power cable, and remove the two bolts on the rear panel. Remove the panel by levering it up then lifting the panel up and away. Plug in and power on the unit—BE EXTREMELY CAREFUL WHILE WORKING IN THE REAR WITH THE UNIT PLUGGED IN. Look for the KS1 relay, using a multimeter, check across post 1 and 2: when the temperature controller has OUT lit the relay should show 220/230VAC, when the temperature controller does not have the OUT lit the relay should have no power across the post 1 and 2. f the relay isn’t working correctly, it will need to be replaced, contact InstroTek for replacements.