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Parts for Whirlpool GU2400XTPT3 Dishwasher - AppliancePartsPros.com

See the attachment for the tech sheet.

Sounds like a water heating problem.
The unit is waiting for the water to heat up and reach a set point temperature and for some reason it is not doing this.

First try removing power for a couple minutes to see if this will reset the unit.

If this does nothing.
Remove power from the unit and check the hi-limit thermostat. It should be 0 ohms.

If OK
This step might be easier if you check it at the control board as you would probably have to pull the dishwasher out from under the counter to check just the heating element.
Unplug the unit and remove the inner door cover so you can get to the control board.
Check from P6 to the W-V (white/violet) side of the door switch.
Should be around 20 ohms.
Note that this checks the heater and the hi-limit thermostat.

IF OK
With power still off check across the door switch.
Should be 0 ohms when activated.
Also check that the latch is OK to be sure that the switch does close when the door is closed.

If OK
Check the thermistor, it is what measures the temperature.
P2-2 to P7, see the wiring diagram for the spec.

If OK then odds are that the control board is the problem.

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.
4. When you start always short the meter leads together. This will tell you that the meter is working and if there is any 0 offset.

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

Ok, I finally found time to open up the dishwasher. For all of the checks that involve the control panel, am I disconnecting the relevant wire first or leaving it connected? And then am I checking the wire or the control board pin? I didn't see instructions on the sticky topic for those types of checks - just isolated component checks.

[COLOR="Blue"]Thermostat was a bit of a pain to get to, but I removed it and it tests at 0 or just above 0 (0.1, 0.3 and so on)[/COLOR].
Looks OK
[COLOR="Blue"]
It showed 10 ohms. Wiring diagram lists a range of 10-30 for this one, so I think that means it's okay. Let me know if not[/COLOR]
Looks OK

[COLOR="Blue"]Couldn't quite figure out how to test the door switch.[/COLOR]
Make sure that the switch is activated by the latch.
Pull both wires off the switch (should ba a white and a white.violet.
Should measure infinite ohms.
Now manually activate the switch, should drop to 0 ohms.

[COLOR="Blue"]Tested P2-2 to P7 again for the thermistor and still nothing. Assuming that means the thermistor is bad and I should order a new one?[/COLOR]
Yes it does as long as you were using the correct meter scale (high enough) (200 K scale).
One thing to note is that it also could be an open connection wire from the control board to the thermistor.

[COLOR="Blue"] Assuming so, does it have another name besides thermistor, because I'm not finding a thermistor in the parts diagrams for this model.[/COLOR]
They call it a thermister (item 25 in section 08)

Yes the switch looks like it is toast.
I would replace it.
Be sure to clean the connector on the wire as best you can so it makes good contact to the switch lug.

I think you are on the wrong meter scale not 200 but 200K which is 200,000 ohms.