Model #KUDI02FRSS1, this tall tub dishwasher simply went dead during the last wash cycle leaving water in the tub and no lights on the display. The customer checked the circuit breaker making sure the unit still had power, and even verified the electrical connection inside the junction box. Not knowing where else to turn, I was given a call to get this unit washing dishes again.



Dishwashers are pretty simple in their operation and although they can vary greatly in design from one to another, most share some rather common dishwasher part placements. Because of this similarity, as we look for failed components or investigate problems in the unit, we can draw some basic conclusions along the way. The most basic of these comes when given a unit that is no longer working, as we simply need to follow the power through the wiring until it disappears. Where it stops is usually going to be the source of the failure. But even simple problems can be oversimplified, as I will point out in this post.

The dishwasher was indeed not working as indicated by a display with no lights. The symptoms provided by the customer were it was working fine, but stopped when they used it last. There was water in the tub, which should provide us a clue, but nothing else seemed wrong. I verified voltage from the outlet to the junction box, just like the customer, then moved on to the control board.

Most dishwashers will use an electronic control board, or timer to provide for cycle operation. Power enters at the electrical connection, usually near one of the front corners, then flows to the control portion of the appliance. From there, it will go to each component during the wash. With voltage at the junction box, the board was my next check. Following the wiring diagram, voltage goes to a thermal fuse, then to the board to provide operating power for the display and logic circuits. That is where I found voltage on one side of the fuse but not on the other, indicating an open circuit. Just to clarify, if you read source voltage when measuring across a fuse like in the photo above, the fuse is bad because you are reading the potential difference from one side to the other. A good fuse would measure 0 volts because there is no potential difference.

With the problem located, I replaced the thermal fuse and had the dishwasher working allowing me to drain the water and run a test cycle. A quick bit of information on thermal fuses. Most have a current and temperature rating for when they will open the circuit. Remembering, anytime we have a high current draw due to excess resistance in the circuit, heat will be generated, so these fuses may open due to actual heat from say the heating element being stuck on, or due to a high resistance connection in the circuit.

The reason I mention this is, remember the dishwasher still had water in it when it failed. This could just be a coincidence, but it is more likely that the failure occurred during a point in the cycle when current draw was high such as the motor and heating element in operation at the same time. Knowing this allows us to dig a little deeper into the failure, and ensure that we identify the reason for the failure, and not just replace the part.

Following this logic, I examined the entire heating circuit and each connection in particular for any possibility of a warn or damaged connector that could result in higher than normal resistance. This could be anywhere in the circuit, but most likely at the thermal fuse connector themselves. Any type of loose connection will add resistance during use, and make for hotter temperatures while in use.

Since the circuit checked out OK, I made sure the terminals of the new thermal fuse were clean and applied a little pressure to the terminal connectors, just to ensure they were tight. After putting it all back together and running some quick tests, I turned it back over to the customer to get going on their pile of dirty dishes.

It is possible the thermal fuse just failed while in use, but it is always good practice to investigate the reasons for a failure, or you may be changing the part again very soon.

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