Miele G1022 giving brief pulses of power to water heater

[Transistor]

My Miele G1022 stops washing with three Wash / Rinse, Drying and End LEDs flashing at 1 Hz.

• Heater element is 25 Ω. That looks OK.
• Thermistor is 13 kΩ at room temperature and 2 kΩ in a cup of boiled water. That looks OK.
• The Schrack 0419 11 0101 02 relay shows scorching on the inside of the case but is working. I’ve hooked up a mains LED lamp in parallel with the element and it’s switching OK but only in short pulses (see below). I’ve also tested operation with a small Siemens contactor with the same result.
• Pressure switch contacts are changing over when I blow into it and check continuity. (I can do about 0.2 bar / 3 psi). This looks OK.
• Flow meter reed switch is switching when filling. This looks OK.

When I test the machine on a 40°C cycle I get this:
m:ss (time)
0:00 Start drain.
0:28 Water in.
2:00 Start wash.
2:07 0.5 s flash on my heater monitoring lamp.
2:12 Stop.
2:22 Start wash.
This start wash sequence repeats 13 times and the error signal turns on at 6:30.

Accessing the diagnostics as I have documented on another thread, How to display the Miele G 1022 fault code, I am getting five flashes which (I think) indicates a U5 fault. The G1000 / G2000 Technical Information (which is the closest I could find) says: [INDENT]U5. Y5, EGS valve: The EGS valve is activated for 60 sec.[/INDENT]

I’ve found the circuit diagram inside the front door. According to it Y5 is the water hardness solenoid. I’m not sure how they’d detect if that’s working or not and it seems an unlikely reason to fault out the whole machine. It’s hardly likely to be a rinse aid float switch error is it?

Bump! I’m still washing up by hand. Does anyone have any ideas for me to try?

[electrofix]

i dont think U5 is a fault it indicates the component being tested

but the manual is not very clear is it

Dave

[Transistor]

Bump! I’m still washing up by hand. Does anyone have any ideas for me to try?

[electrofix]

you know the more i look at this the more i think it may be a power supply problem on the board.

lets rewrite your sequence

m:ss (time)
0:00 Start drain.
0:28 Water in.
2:00 Start wash.
2:07 0.5 s flash on my heater monitoring lamp.
board runs out of power to supply everything the heater relay is just the straw that breaks the camels back.
2:12 board crashes amd machine stops
2:22 power supply recovers after crash and starts to wash
heater comes on again and board crashes etc etc etc
This start wash sequence repeats 13 times and the error signal turns on at 6:30.

[Transistor]

I’ve made significant progress with diagnosis capability but not with solving the problem. I have figured out how to read the fault codes and how to run the various component tests from the front panel. The results are:

• Everything seems to work in test mode.
• In run mode I get an F24 error. The service manual I’m using says that this is a heating relay contact fault but the heater is turning on. (I’ve proved this by wiring a lamp in parallel with the element and in the service mini-program.

I’ve run the test sequence mini-program U1 (section 6.2.1.3 of the manual) and the water warmed up.
The heater / pressure switch is switching. (I continuity checked the double-pole changeover contacts change over when I blow into the switch. I can do about 0.2 bar / 3 psi.)

Anyone?

[electrofix]

from the look of the info on an F24 fault the heater relay is shown as a changeover contact arrangement. it is the un energised contacts that are used to determine if the relay is in the open position
it talks about the resitace being above 10 meg and if its not it throws up a code. . any signs of water or damage on the relay or pressure sw contacts
is the heater got any earth problems. not enough to blow your trip but enough to upset electronics. Try disconnecting heater and put a lamp across it but not an LED one something that will give a decent load

Dave

[Transistor]

Thanks again, Dave.
I have the schematic diagram and had figured out that they were checking the relay.

Figure 1. Detail of heating relay and pressure switch shrunk to satisfy the 19.5k filesize limit!

I’ve replaced K1 with a Siemens contactor for test purposes. I’ve done a continuity test on the level switch and confirmed that the changeover contacts NO and NC are working when I blow into the switch. I’ve checked for continuity from B1/13 (pressure switch) pins 12 and 22 up to the control board connector. All OK.

Response to your comments:

From the look of the info on an F24 fault the heater relay is shown as a changeover contact arrangement. it is the un energised contacts that are used to determine if the relay is in the open position. It talks about the resistance being above 10 meg and if its not it throws up a code. . any signs of water or damage on the relay or pressure sw contacts.

No all looks OK.

Is the heater got any earth problems. not enough to blow your trip but enough to upset electronics. Try disconnecting heater and put a lamp across it but not an LED one something that will give a decent load.

The heater seems OK. I don’t have a Meggar but a resistance test between the element terminals and earth is over-range. A test lamp lights up in the test mini-cycle and the water heats.

I’m beginning to suspect a control board fault. It may be time to give up and purchase a new one but it seems a shame when everything looks in good condition.

[electrofix]

have you checked the motor pressure switch contacts to earth and between open contacts

had a few of these with diaphram problems, normally get so wet inside it pops the trip but what if its leaking just enough to get it damp ?

long shot i know

Dave

[Transistor]

You were correct to be concerned about the level / pressure switch. I opened it up and found that the rubber diaphragm has a small leak. I don’t have spare so I peel open the housing carefully, cleaned it up, cut a second diaphragm from a bicycle inner tube and reassembled it. I did a full continuity test and it operated properly when blowing into one port with the other one plugged.

I now have the machine on test. It is filling and draining in a continuous loop. I have run the service mode mini-test cycle and the pump main works OK but it doesn’t come on in a regular cycle. I’ve cleaned the water intake filter and restrictor and checked that the impeller reed switch voltage is changing during filling.

Any more ideas?

—-
How do I get more upload space for images on this site?

[electrofix]

images can be uploaded to an external site then post a public link

its all due to the cost of server storage i am afraid

Dave

[electrofix]

so you switch on and both inlet valve and pump come on together ?

Dave

[Transistor]

No, inlet valve cycles on-off-on-off until there is about the right volume of water in the bottom of the chamber and then it pumps out to drain and the cycle restarts. I’m expecting the main pump to start and check if the the pressure switch changes state to indicate that there is adequate water present to run a cycle but it doesn’t seem to – it just drains again.

• While water is flowing in the Fill / Drain LED is steady red.
• During the pause in in-fill the Fill / Drain LED is blinking.
• During drain the fill cycle is continuing.

It’s very strange.

Thanks again for sticking with me on this. I’m developing an unexpected level of intimacy with every component of the dishwasher at this stage!

[electrofix]

did anything get wet while you stripped it down
you have to remember there is salt in a dishwasher so it can cause electrical conduction if it gets on plugs and sockets

also just as an after thought, are you sure all the wiring went back correctly ?

Dave

[Transistor]

All dry and all hooked up OK. (I’m an industrial automation engineer so this should be within my capabilities! It’s been rather frustrating.)

[electrofix]

it does sound like it cant see the water filling. double check the reed switch and its connection to the board. I would continuity check it just to be certain

every time we find something another problem crops up

Dave

[Author]

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