Here are your parts
Replacement parts for WHIRLPOOL DU1145XTPB6 Undercounter Dishwasher | AppliancePartsPros.com

Here is the tech sheet
http://www.servicematters.com/docs/wiring/Tech%20Sheet%20-%208535451.pdf

Can be a number of things: the heater itself, the hi-limit thermostat, the thermistor or the board itself. If the dishes are drying correctly, the the first two item are unlikely.

First remove power from the unit for half an hour or so to see if it will reset.
Try diagnostics in the tech sheet.
Measure the components with a meter.

If you do not own a meter, I would suggest you purchase a one. You can get a decent digital multimeter for under $20.00. You do not need fancy though it is nice if the leads are a couple feet long.
If it saves ordering one unnecessary part it has paid for itself and you end up owning a useful tool.
Most places will not let you return electrical parts so if you order it, you own it.
A couple things to watch when measuring ohms and continuity
1. Always remove power from the machine otherwise you could blow your meter.
2. Always disconnect at least one side of any device you are checking. This eliminates the possibility of measuring an alternate/parallel circuit path.
3. When checking for closed contacts and continuity use the lowest scale (Usually 200 ohms). Then try higher scales. This scale is 0 to 200 ohms so if the device you are measuring is 300 ohms this scale would show an open circuit which it is not, you are just measuring outside the scale's dynamic range.

There is a good STICKY at the start of this forum about it's use.