Although there are several factors that could be affecting your dishwasher heating, the most common part associated with dishwasher temperature problems is the heating element. Even in high quality parts it is common for the wires to burn out. You can use a multimeter to assess whether or not a part needs to be replaced – this measures element resistance, which should be between 15 and 30 ohms. A reading above 30 means the element needs to be replaced.
Luckily this situation is a fairly simple and relatively inexpensive fix (compared to the cost of hiring a handyman). Here is a step-by-step guide for this doable DIY dishwasher fix. You will need a new heating element, a multimeter and a basic toolset.