Questions about dishwasher thermostats

Dishwasher Repair
1

Hi,

I have some questions related to my dishwasher’s thermostats.

First, some background.

I have a problem with the dishwasher getting stuck in the wash cycle. This happens in both the pre-wash and the main wash at the point where the water is being heated up. I believe the heater is working correctly (though I didn’t measure the temperature) from the following 2 pieces of evidence:
1 - during the more than 1 hour that the cycle was “stuck” (and before I manually advanced the timer knob), there was steam coming out of the door vent and the door’s vent opening has turned white from the heat (this is a black colored door).
2 - I measured continuity on the hi-limit thermostat and about 18 ohms on the heater coil.

With that background, I’ve got a couple of questions concerning the 2 thermostats in this machine.

First question: I pulled the “temp boost” thermostat and tried to detect when the thermostat would close by pressing it against an stainless steel electric kettle while it was boiling water. I saw that the thermostat closed at a point just before the water reached the boiling point. Is it possible that the thermostat’s “trigger” temperature could have drifted to a higher threshold? Would this be an expected failure mode?

Second question: I understand that the hi-limit thermostat is designed to go open-circuit when the heated water exceeds a certain temp threshold. Would this happen in normal circumstances (i.e., like in an electric kettle)? Or is this threshold temperature only reached during failure scenarios? I’m wondering if its possible for this thermostat to be opening the circuit too early (i.e., before the “temp boost” thermostat has a chance to close)?

As a last test, I pulled the “temp boost” thermostat and ran another wash cycle. After waiting at the water heating stage for a while, I shorted the 2 wires where the thermostat would go. The cycle then continued as normal.

So do I have a bad “temp boost” thermostat? Or hi-limit thermostat? Or both?

Any help/suggestions would be really appreciated!

plumb_lost

2

Sounds like the thermostat which you called “temp boost” is bad but to tell you exactly I would like to see the wiring diagram. Can you post it? Also the model number you posted is incorrect.

Gene.

3

Hi Gene,

Thanks for the reply. The model number is right; it was purchased in '94 in Canada. See photo below.

The schematic was on the door; it’s kind of wrinkled. I’m not sure if that’s because of the glue running when things got hot.

Is it expected that the thermostat threshold to shift up like this if it is failing?

Regards,
plumb_lost
DSCF1927.jpg (66.7 KB)
DSCF1934.jpg (127.2 KB)

4

I can not read on the diagram if this “temp boost” thermostat shown as a NO (normally open) or NC (normally closed). If it’s NO then you have to replace it because it’s not reading the correct temperature.

Gene.
Unfortunately there is no on line access for non American models.