Miele dishwasher (G1143) repair / suspicious pressure switch (solved)

[max.wwwang]

Yet another repair project. Miele dishwasher with Wash/Rinse, Drying and End indicator lights flash simultaneously. Shown in photos with highlights captured from the user manual.

The suspected culprit is a faulty pressure sensor - also shown in photo. Suspecting because its behaviour (when testing with DMM) does not make sense. Here is what I got with it:

•   No connections between terminal groups I and II (which seems about right)
•   1/3: normally closed, open when P1 is triggered (about right)
•   4/5: always closed (P1/P2 triggered or not) (probably a fault)
•   There is no effect when triggering P2 (probably also a fault)

I guess ports P1/P2 are probably for sensing 2 different levels of pressure.

Does anyone have experience with it (such as having tested a working one)? Or thoughts regardless? Insights appreciated.

If it's indeed faulty, the machine is not worth repair. A new part costs around $200 or more!

[max.wwwang]

Tests/attempts made:

- Inlet filter checked and is ok.
- Drain hose flushed clean without blockage.
- Temperature sensor (NTC) looks good.
- Reset to factory default settings is done, no cure.

[Haenk]

ebay Germany has offering of below 40 EUR used, 100 EUR new.
I as well found a refurbishing service, which replaces the internal membrane. So a defective membrane is the likely issue, I would say.

[max.wwwang]

ebay Germany has offering of below 40 EUR used, 100 EUR new.
I as well found a refurbishing service, which replaces the internal membrane. So a defective membrane is the likely issue, I would say.

Thanks for the info. 100 Euro is still about NZ$170. 
Good to have used for sale though, and refurbishing! Save the planet, and our money.

If it can be confirmed as faulty, I will tear it down and see exactly how it's constructed and wired internally, so potentially can help some people out there down the way.

[Hamelec]

you have seen   at 3:00 ?
then you know how the internal switches are connected to the terminal

[max.wwwang]

you have seen at 3:00 ?
then you know how the internal switches are connected to the terminal

Thanks. That's what I thought. So the behaviour I got is definitely faulty.

Interestingly, this video does not even mention three terminals for each switch (briefly shown at 0:53). Useful but can be much more useful.

[Hamelec]

can you hear a click of each of the switches if you apply pressure?

if yes you should test the switches with mains voltage and a bulb..

[max.wwwang]

can you hear a click of each of the switches if you apply pressure?

if yes you should test the switches with mains voltage and a bulb..

The one at P2 gives clicking sound. P1 does not.
I tested with DMM for connectivity, as in OP.

[Haenk]

Even better, the membrane is available as a spare part:
https://www.ebay.de/itm/235200461263

(However all offerings of this membrane seem to lead back to only one seller; not sure if he does ship outside Germany...)

[Hamelec]

may be you applied too less pressure for testing?
you will need 0.07bar for the 1st and 0.11bar for the 2nd switch..
(700 mmWS / 1100mmWS)

[max.wwwang]

Even better, the membrane is available as a spare part:
https://www.ebay.de/itm/235200461263

(However all offerings of this membrane seem to lead back to only one seller; not sure if he does ship outside Germany...)

This is nice! The problem though is that the membrane is not intended to be replaced, because the encapsulation of the part is one-off, not re-doable.

may be you applied too less pressure for testing?
you will need 0.07bar for the 1st and 0.11bar for the 2nd switch..
(700 mmWS / 1100mmWS)

I pressed the membrane with a stick. I thought I used enough force, but after another try; I didn't - when pressing really hard, it also clicks! (So clearly this one is for 1100mmWS.)

Nice inference on the pressure settings. That's exactly what I thought it should be (two triggering pressure levels), though I didn't get what the numbers meant. Now it makes good sense.

[max.wwwang]

After applying more pressure, the new findings are:

•   No connections between terminal groups I and II (which seems about right)
•   1/3: normally closed, open when P1 is triggered (about right)
•   2/3: normally open, closed when P1 is triggered (about right)
•   4/5: always closed (P1/P2 triggered or not) (probably a fault)
•   There is no effect when triggering P2 (probably also a fault)

If the marking "700 mmWS / 1100mmWS" means water pressure of 700mm and 1100mm, then (based on the forces needed in testing) P1 is the high pressure switch, triggering at 100mm water head, whereas P2 the lower pressure switch at 700mm.

Certainly it's faulty, so will be torn apart.

[max.wwwang]

Tore the thing apart. Now everything is under sunlight without mysteries. My guess was not exactly right, which fooled me a bit. Now findings and understandings are:

•   The two ports P1/P2 lead to a common chamber with a membrane and a rigid plastic backing actuator plate behind it.
•   The triggering pressures of the two switches appear to be (intended to be) identical. (Why two identical switches? Probably for error tolerance.)
•   Both switches are arranged symmetrical about the case (left and right) despite the asymmetrical arrangement of the ports.
•   For mechanical reasons, the switches behave in a way similar to Schmitt triggers, triggering at pressure levels 700mm and 1100mm water head.

[Edit] I've done further tests double check. Refer to the schematic in the post below.
•   The way the control module detects if this invalid condition of the pressure switch is present is like this. When a program starts, DC 12V is sent briefly to the relay allowing mains AC to present on its terminals 3 and 4. If the pressure switch is working, since the circulation motor is now not working so no pressure present, mains voltage will present on terminals 1 and 6, which is detected by the control unit.
(To check this theory, I hooked a DDM across the 12V DC wires, and pulled out one of the two wires from the pressure switch going to the control unit. After pressing the Start/Stop  button to start a program, I can see the DMM detecting a brief presence of 12VDC. After a while, the three LEDs start flashing and the machine stops working.)

I hope this information is clear and thorough to anyone in the future who needs to find out if it is faulty.

In my case, the control unit probably detected the faulty condition, when 1/3 and 4/5 are closed, respectively, which is not a valid condition. But I will investigate further.

[max.wwwang]

Played around the disassembled switch for a while and now it seems to work the way intended, though I'm not able to put it back to its capsulated form. The previous problematic behaviour was probably due to the membrane leaking allowing water to get into the switches.

But it's now sufficient for a test. Having it temporarily taped up and put back into the circuit, turn the switch on, the three LED flashing simultaneously error is gone. I can hear the solenoid on the inlet switched on allowing water to come in.

Another observation is that if I manually trigger the bottom tray float switch (which will immediately turn on the drain pump) and hold for a while, the three LEDs will also flash. This means the same symptom may be caused by at least two different problems: 1) leaking to the tray; and 2) a faulty pressure switch.

This can be considered as mission accomplished. 

[Edit] To make this thread complete, I've drawn up the schematic of this model (please expect and excuse what might be inaccurate, omission, or non-conformance to the standard of schematics), and taken photos of its main control board - all attached below for future reference.

[adinsen]

Great read! If the switch fails again, I suggest reassembling it with a little silicone grease on the edge of the membrane. Silicone grease is easy to work with and does wonders keeping water out of things.

[max.wwwang]

Great read! If the switch fails again, I suggest reassembling it with a little silicone grease on the edge of the membrane. Silicone grease is easy to work with and does wonders keeping water out of things.

Thanks for the tip! Another thought I had was (which came out of this case), when this switch fails but if the membrane is not broken (just like this one), it can be pulled out and thoroughly cleaned (not too difficult since it has two ports), and let any water ingress into the dry side completely dry. In combination with the silicon trick, it may work fine for a good time without requiring a replacement.

[Edit] Wait, silicon probably is not good. The reason is that, since the pressure-sensing chamber is connected to the water-circulating system doing the washing, silicon will contaminate the water and the dishes I guess. 

[oliviamills140]

Certainly! It seems like you're dealing with a Miele dishwasher issue where the Wash/Rinse, Drying, and End indicator lights flash simultaneously. The suspected cause is a faulty pressure sensor based on your observations with a digital multimeter (DMM). The behavior you've described, such as no connection between terminal groups I and II and anomalies in the status of terminals 1/3 and 4/5, suggests a potential issue. If the pressure sensor is indeed faulty, and considering the cost of a new part is around $200 or more, you're questioning whether it's worth repairing the machine. If you need further assistance or insight, feel free to ask.

[max.wwwang]

Certainly! It seems like you're dealing with a Miele dishwasher issue where the Wash/Rinse, Drying, and End indicator lights flash simultaneously. The suspected cause is a faulty pressure sensor based on your observations with a digital multimeter (DMM). The behavior you've described, such as no connection between terminal groups I and II and anomalies in the status of terminals 1/3 and 4/5, suggests a potential issue. If the pressure sensor is indeed faulty, and considering the cost of a new part is around $200 or more, you're questioning whether it's worth repairing the machine. If you need further assistance or insight, feel free to ask.

Thanks for your post and for your offer of assistance. In this case, I've got to the very bottom of the issue, so all sorted. 

[amyk]

Certainly! It seems like you're dealing with a Miele dishwasher issue where the Wash/Rinse, Drying, and End indicator lights flash simultaneously. The suspected cause is a faulty pressure sensor based on your observations with a digital multimeter (DMM). The behavior you've described, such as no connection between terminal groups I and II and anomalies in the status of terminals 1/3 and 4/5, suggests a potential issue. If the pressure sensor is indeed faulty, and considering the cost of a new part is around $200 or more, you're questioning whether it's worth repairing the machine. If you need further assistance or insight, feel free to ask.

Thanks for your post and for your offer of assistance. In this case, I've got to the very bottom of the issue, so all sorted. 

You just replied to an AI-generated post that looks like it was copy-pasted verbatim from ChatGPT.

[max.wwwang]

You just replied to an AI-generated post that looks like it was copy-pasted verbatim from ChatGPT.

Chatbot, come on in. Take a seat and make yourself comfortable.