Miele Dishwasher Error F78 - Circulation Pump issue

Things that have worked for me with f78 error: once; took bottom spray arm off and poured hot (not boiling) water down hole, this cleared a blockage. Many times; drained machine and examined grill over channel at back, if this has anything at all in it, eg tiny hairs, clear plastic, eggshell, get it all out - a cake fork works quite well, the machine should then work. When the machine activates its pump it looks for a current down the channel at the back and shuts off with f78 if it doesn’t detect one. Small obstructions in the channel can obstruct the current and make the sensor think the pump is not working. This is a design flaw with this machine as the plastic grills over the channel are insufficient to stop things getting through them, and may make things worse because thin strips etc can drape over them and are then impossible for the machine to dislodge itself.

the ( most frequent) problem which causes this fault in my machine is a blockage in the pump sensor channel. With the machine turned off and the racks, spray arms, filter etc, taken out, drain the broken machine as much as you can, using ladle or small container. You can see a channel covered with white grill bars at the back. This is the channel that takes the current of water from the pump to the sensor that tells the machine that the pump is working. Examine the channel carefully, you may need a torch. If you can see anything at all in this channel or draped over the white grill bars, then you need to get it out, in my house our smallest forks are the right width to fit between the grill bars. Once the channel is clear put the machine back together and restart it, the error should have cleared and the machine’s cycle should work without F78.

The second most common problem, but much less often is a blockage. If you have checked the pump chamber and it is clear then try pouring hot (not boiling) water down the bottom spray arm hole, it should come out and fill up the bottom chamber. If the water backs up and then goes through in a rush you have cleared a blockage. Be aware that the water in the bottom of the machine will now be very hot.

If blockages in the sensor channel or elsewhere are happening it means that residue is getting though the machine’s filter. Make sure the filter and stainless steel mesh are clean, and there is no residue on the plastic where the stainless steel mesh sits which might be stopping it sitting flush against the bottom of the machine.

You may also want to clear very heavy residue off pots etc before putting them in the machine. My wife tells me I don’t do that very well, which is why we only ever get this error when I have stacked it.