This problem is commonly caused by a water inlet valve (also known as a mixing valve) leaking by. If you live in an area that has hard water, or if you use well water, sediment, rust or calcified deposits can accumulate in the inlet valve and cause it not to close properly. Usually when they start leaking, you need to replace them. The following link explains how to access and replace the valve:
If the model number is correct, the part number for a replacement valve is 285805.
If you have any questions, please post back and let me know. I hope this helps you.