Error F78 on a Miele dishwasher

The common error F78, issued by the Miele PMM, indicates a malfunction of the circulation pump. The issue may be either a breakdown of the pump, or a breakdown in communication between it and the electronic module. To find out why the code appears, you will have to partially disassemble the dishwasher and check the part. We'll tell you how to do this.

What to check first?

What should I do if I see this error code on the display of my Miele dishwasher? In 75% of cases F78 indicates a malfunction of the circulation pump, usually its frequency converter. This is a small part that coordinates the operation of the pump. Usually the board is damaged due to a strong voltage drop in the electrical network.

If the frequency converter malfunctions, the pump cannot be repaired; in order to reset the error and revive the dishwasher, you will have to change the assembly. However, it happens that the board is intact, and the reason turns out to be a broken impeller, which can be repaired, or worn out bushings.

Error F78 indicates a violation of water circulation in the system; you will not be able to operate a Miele dishwasher that issues such a code.

The user’s task is to get to the circulation pump and check the part. The algorithm of actions will be as follows:

• Unplug your Miele dishwasher;
• turn off the tap responsible for supplying water to the machine;
• disconnect the PMM from communications;
• open the machine door, remove the dish baskets from the chamber;
• remove the garbage filter from the hopper and remove the mesh;
• Unscrew the screws securing the circulation pump block, remove the rubber seal;
• 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 PMM pan;
• unhook the inlet pipe;
• find the pump, disconnect the wires from it, disconnect the pipes;
• Having dealt with the fastenings, remove the pump from the machine.

The next step is disassembling the circulation pump. In fact, the pump is quite easily divided into its component parts. We'll tell you what to do next.

Disassembling the dishwasher pump

To fix the problem, it is necessary to disassemble and inspect the PMM recirculation pump. All components are removed in stages. First of all, the nozzle on the rotor of the part is screwed together.

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

The further algorithm will be as follows:

• remove the impeller from the shaft;
• remove the cover covering the anchor;
• drain the water that is in the glass;
• pull out the anchor;
• remove the plain bearings;
• put the new bushings in place;
• Reassemble the pump in reverse order.

If the problem is a damaged impeller, then you can also try to do without replacing the unit. Moreover, the cost of new circulation pumps for Miele dishwashers, regardless of the model, is high. Therefore, many users prefer to repair the pump in all possible ways.

The “collapsed” impeller of the PMM circulation pump can be restored using a soldering iron and plastic welding rods.

The situation when the impeller breaks into two parts occurs quite often. This is a typical problem with PMM heat pumps. To connect two blocks together, you will need a 3 mm drill, a soldering iron and plastic rods for welding. Necessary:

• 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 the bottom and top.

It happens that during the dismantling process the “nose” of the impeller accidentally comes off. That is, the part with which the part rests on the end of the rotor shaft. In this case, it is necessary to put a stainless steel washer of a suitable size on the shaft.

Alternatively, you can 3D print the upper and lower halves of the impeller. Craftsmen sell similar parts, their cost is low. Just bring a sample and a specialist will make a similar spare part for your Miele dishwasher.

Thus, the pump can be repaired if there is mechanical damage to its components: the impeller or bushings. When the problem is electronics, namely a breakdown of the frequency converter, it will not be possible to repair the pump. You will have to buy and install a new element.

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