Kitchenaid KDM21 overheat

[antiquetvguy]

My Kitchenaid KDM21 Monterey went into the final dry cycle today and I started smelling a burning smell. I opened the dishwasher to discover the heating element was RED HOT. I could hear the blower fan running, but evidently what ever controls the drying temperature was not cycling the heating element off and on. There was nothing (no plastic etc.) sitting on the heating element.

In addition, I dumped several pitchers of water into the tub to cool off the heating element. Then I hit the cancel button to pump out the water and reset the cycle timer so I could run a test cycle. I used the pot scrub cycle so that I could watch the machine fill with water and go through the water heating. The heating element incicator light never turned off and just keep heating the water until it was near boiling, at which point I shut the unit down. Normally the water heating indicator goes out after a few minutes.

What controls the drying cycle temperature and the water heating temperature? I know there are 3 thermo discs. 2 are on the left side of the tub mounted on a copper stud, and one disc is in the front of the tub. It also appears there may be a retrofit kit FSP4163588 that has all 3 thermo discs as a unit. But I am not sure if the original thermo discs are the issue. I saw somewhere, that there also might be some sort of temperature control attached to the drying fan assembly.

Unfortunately I do not have a service manual that describes the function if each individual thermo disc, or if there is some temperture control in the drying fan assembly.

Does anyone have a clear knowledge of what does the control of the heating element during drying and water heating. Are all 3 thermo discs of the same type or is each one different? And what does each thermo disc do?

Thanks in advance for your technical assistance.

 

[eronie]

Sounds to me like a timer problem. The element in the bottom of the tub should not be on during the dry cycle, that's a separate fan, heater.

 

[antiquetvguy]

Thank you, your input about the separate fan heater. That gives me more food for thought. I am going to run another full cycle to verify that it was in drying cycle when I found the red hot water heater element. However the heating element is remaining on during the water heating part of the cycle and evidently not detecting when the water is up to proper temperature. So maybe I have a problem with the water temp thermostats too?? I did order the replacement tri thermostat assembly so when I install that retrofit part, I will see if it operates properly.

It's possible that I was mistaken about being in the drying cycle. I will open the front panel to access the timer. There is a 1/4" square hole in the front of the timer so you can insert a 1/4" square drive and manually advance the timer to various parts of the cycle. I will put it in dry cycle to see if the water heating element is off or on.

 

[combo52]

Red Hot Water heating Element

It is likely it was still in a water heating cycle and just boiled the water away when you found it, check for a bad thermostat or a loose wire, it could also be a timer problem.

 

John L.

 

[antiquetvguy]

Thanks! I will report back when the new parts arrive and I install them.

 

[antiquetvguy]

Trouble shooting Overheat Update

Reading the manual for the Monterey 21 I got some information on the operation of the water heating cycles. During normal water heating, the tub fills without pump re-circulation. When the water is heated up to temperature (140 degrees) the heating element stops and then the pump start.

There is also a optional SANI-RINSE function that can be added by pushing that button to any of the wash cycles. When SANI-RINSE is selected, it adds a rinse water preheating cycle to the last rinse cycle. The manual says that in the SANI-RINSE water heating period the water is heated to 165 degrees prior to the pump starting. So there must be a 140 degree and a 165 degree thermo disc on the water temperature sensing assembly.

I failed to mention in my first post, that my wife had selected the SANI-RINSE function when I discovered the red hot eating element. The puzzling thing is that there was no water in the tub when I found the element red hot, and I now believe that the unit was probably in the last rinse cycle in SANI RINSE mode trying to heat the water to 165 degrees. This complicates things. I can't understand why the heating element would be energized and have no water in the tub, unless there was a mal-function of the inlet water valve solenoid, or perhaps if the float switch failed to close (bad switch or float stuck in the up position)

My next step is to run the machine through a regular cycle with the SANI-RINSE option turned on to see if I can duplicate the mal-function and see if the tub fills with water during the last SANI-RINSE rinse cycle.

I will update again after I monitor the SANI-RINSE cycle.

I received the retrofit thermostat kit but it was missing a copper washer and an "O" ring needed for the installation. So now I have to try to find some generic parts to replace the missing ones. Photo below.

 

[combo52]

There is a 140 and a 165 thermostat plus a safety that should shut down the heater if it runs dry for very long in that package.

 

I would run it again on Sani rinse and see what happens, it is very common for fill valves to fail near the end of the cycle as they get hot and to work again after they cool, so run the full cycle and observe.

 

It is also possible that the heater evaporated all the water in the sump if it got stuck on the 165 thermostat long enough.

 

You can reuse the washer and seal from the original thermostats to install the new parts.

 

John L.

 

[antiquetvguy]

After much time doing observation the darn dishwasher failed again. This time I was able to watch the timer to see if it had a problem. I discovered that the ratchet pawl that advances the toothed main cam gear, was evidently sticky and the pawl was not engaging with the toothed gear. So the timer was not advancing. I pulled the timer, freed up the ratchet pawl with a silicone spray and ran the timer motor on my test bench over night. So far it hasn't missed a beat.

Thanks to eronie and combo52, you were correct with your suspicion of the timer. Looks like we're good to go for another 20 years if I live that long.

 

[combo52]

Yay Glad It Seems To Be working again

It is often amazing what a little of the proper lubricant can do in the right place.

 

John L.