My Frigidaire Ultra quiet III heating element works only on light wash

I recommend that you check the water fill level first. Start a cycle and then crack the door open once the filling stops. Open the door fully and look at the water level in the bottom of the tub. The water should be within 1/4" to just touching the bottom of the heating element. If it is too low, then fixing the fill problem in the dishwasher may resolve your problem. Reply with additional details if you need help with that issue.

If the water is filling properly, check to see if the heating element is working. Do not touch it directly. You should be able to determine whether it is heating by placing your fingers close to the element when it is in the water heating portion of that cycle. If the element is not heating, then you may have a bad element or a problem with the control board. A wiring failure could also prevent the element from heating.