Miele dishwasher error code F78

The common error code F78 displayed by Miele dishwashers indicates a faulty circulation pump. This could be due to either a faulty pump or a communication problem between it and the electronic module. To determine the cause of the code, you'll need to partially disassemble the dishwasher and inspect the component. We'll explain how.

What to check first?

What should you do if you see this error code on your Miele dishwasher display? In 75% of cases F78 indicates a malfunction of the circulation pump, usually its frequency converter. This is a small component that coordinates the pump's operation. The board is usually damaged by a severe power surge.

If the frequency converter malfunctions, the pump cannot be repaired. To reset the error and restore the dishwasher, the entire unit must be replaced. However, sometimes the board is intact, and the cause is a broken impeller, which can be repaired, or worn bushings.

Error F78 indicates a water circulation problem in the system; a Miele dishwasher displaying this code will not work.

The user's task is to access the circulation pump and inspect the component. The sequence of actions is as follows:

• Unplug the Miele dishwasher;
• turn off the tap that supplies water to the machine;
• disconnect the dishwasher from communications;
• open the machine door and remove the dish baskets from the chamber;
• remove the waste filter from the bin and remove the mesh;
• unscrew the screws securing the circulation pump block, remove the sealing rubber;
• place the dishwasher on the floor;
• loosen the latches securing the bottom of the machine;
• disconnect the contacts of the Aquastop float sensor and remove the dishwasher pan;
• unhook the inlet pipe;
• find the pump, disconnect the wires from it, disconnect the pipes;
• Once you have secured the fasteners, remove the pump from the machine.

The next step is disassembling the circulation pump. In fact, the pump is quite easy to separate into its component parts. We'll explain what to do next.

Disassembling the dishwasher pump

To fix the problem, you need to disassemble and inspect the dishwasher's recirculation pump. All components are removed in stages. First, unscrew the nozzle on the rotor.

In addition to a frequency converter and impeller, the circulation pump of Miele dishwashers contains an anchor, a pair of graphite bushings, and a winding. Sometimes the cause of the error is F78 are worn bushings or plain bearings. You can replace them yourself by printing the components on a 3D printer or by purchasing them from a specialist.

The further algorithm will be as follows:

• remove the impeller from the shaft;
• remove the cover covering the anchor;
• drain the water that will be in the glass;
• pull out the anchor;
• remove the plain bearings;
• put the new bushings in their places;
• reassemble the pump in reverse order.

If the impeller is damaged, you can also try to avoid replacing the unit. Moreover, the cost of new Miele dishwasher circulation pumps, regardless of model, is high. Therefore, many users prefer to repair the pump by any means possible.

A broken impeller of a dishwasher circulation pump can be repaired using a soldering iron and plastic welding rods.

It's quite common for an impeller to split into two parts. This is a typical problem with PMM heat pumps. To connect the two units together, you'll need a 3mm drill, a soldering iron, and plastic welding rods. You'll need:

• connect the upper and lower parts of the mechanism, drill 4-5 through holes around the perimeter;
• insert plastic rods into the holes;
• melt the rods with a regular soldering iron from below and above.

Sometimes, during disassembly, the impeller's "nose"—the part that rests against the end of the rotor shaft—can accidentally come off. In this case, it's necessary to place a stainless steel washer of the appropriate size on the shaft.

Alternatively, you can 3D print the upper and lower halves of the impeller. Specialists sell these parts at low prices. Simply bring a sample, and a specialist will make a similar part for your Miele dishwasher.

Therefore, a pump can be repaired if there is mechanical damage to its components, such as the impeller or bushings. If the problem lies in the electronics, specifically a faulty frequency converter, the pump cannot be repaired. A new component will have to be purchased and installed.

   

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