Here are your parts
Replacement parts for WHIRLPOOL GU1500XTLB1 Undercounter Dishwasher | AppliancePartsPros.com

Here is a manual which should help sort this out.
https://secured.whirlpool.com/Service/SrvTechAdm.nsf/2cd44500d572193285256a45004fd9d6/52521bdbd0ef763c85256cbc00520548/$FILE/8178022.pdf

Element, thermostat or is there are water temp sensor in this model?
Thermostat is a hi-limit Item 30 in Section 7 of the parts
Temp sensor is a thermistor Item 25 in Section 8

If the cycle times are normal I would start with the thermistor.
The unit thinks the temperatures are OK so progresses merrily through the cycle.

If the cycle times are longer, I would remove power from the unit and check the thermostat and heater with a meter. The unit is waiting for the water to get to set point it does not but there is usually a default time where the unit will continue the cycle.
Be sure to disconnect one side of the device you are checking this prevents you from reading an alternate/parallel circuit path.
Thermostat should be 0 ohms and the heater about 20 ohms.

I have same problem with a whirlpool wdt710paym2. It does not heat water or dry it. Just replaced the element as it was cracked but still no heat. Does this apply too?

On the new model dishwashers after heating element burnt out I had to perform a reset to get the heater to turn back on, so pick three buttons. Button 1, button 2 and button 3. Press button 1,2,3 again 1,2,3 again 1,2,3 it should start a diagnostic after it completes the diag (about 10 min) it clears the codes and should start working.