Bosch solid tap light mystery – please help

[leenowell]

Hi all,

Firstly sorry for the long post but I have done a lot of troubleshooting on this and now reached a dead end…. I would greatly appreciate any pearls of wisdom as I am at a loss now.

I have a Bosch SMV50C00GB dishwasher which has developed a fault. When I start the programme it pumps out residual water from previous failed test, starts to fill for a while then starts beeping, starts to empty but interestingly continues to fill. Opening the door and the tap light is permanently on. After a lot of Googling as far as I can make out, there could be a variety of reasons for this so have tested each as follows and still no joy

1. Filters / impeller clogged
Taken all filters out of the inside, cleaned and checked the impeller which was clear and rotates freely when turned. Also removed the filter from the inlet pipe and it is also clear

2. Float switch in the bottom activated
It seemed to be working ok but to be 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} sure I have removed the switch from above the float so there is no way it could be activated but left it connected to the machine. To check it is working, when I start the programme I manually pressed the switch and it immediately interrupted the programme with a flashing tap light. So I believe this proves that the switch is not activated normally and does work when pressed?

3. Water flow insufficient
I have looked at a couple of potential causes of this
a) Water supply itself
It is directly off the mains water supply and never been an issue. Running it in to a bucket seems like high pressure and good flow. Also, I tried another dishwasher on it and it was fine.
b) the inlet valve
I have tested the inlet valve (it is on the end of the inlet pipe where you connect it to the supply) by disconnecting the machine end from the chamber on the side of the machine and running it into a bucket. Water flows ok albeit much slower than directly out of the supply. So thinking that may be the issue, I connected the chamber up directly to the supply. By putting a multi meter on the connector to the valve, I started the programme and when it went to 240v I turned the supply on to fill it. When the beeping started, it remained at 240v so left it fill for a few more seconds thinking it would go to 0v but remained at 240v. I tried this with the supply on full blast and half and same thing happened. So I believe it can’t really be a supply issue.

4. It thinks there is a supply issue
It has a little fan in the water chamber on the side which spins when water is flowing in. It has a reed switch on the outside of the chamber which I believe is used to measure the flow of the inlet water. Removing the little board and testing the reed switch with a magnet and multi meter it looked faulty as when the magnet closed the switch there was a v high resistance. After a few tests it failed completely. So I bought a new reed switch unsoldered the old one and replaced it with a new one. Refitting it to the dishwasher I run some water in with my hose from 3b and using the multi meter I can see the reed switch going on and off as the fan rotates. Connecting the board back up to the dishwasher tested the connector is connected to the reed switch (i.e. connector is working fine) ok and all seems fine.

So after all this, the issue remains the same. Anyone have any ideas on other lines of enquiry I could try?

Many thanks in advance

Lee.

[electrofix]

check wiring from reed sw back to the board

Dave

[leenowell]

Thanks very much for getting back to me Dave – good idea. I removed the relevant connector from the control board, started filling the machine and could detect the pulses from the reed switch so the wiring must be fine. I couldn’t work out how to get to the circuit board itself to confirm that there isn’t a dodgy connection between the connector and the board although seems unlikely.

Given I have now bypassed the inlet valve and removed the float switch, is there anything else that is active that could cause the error? If not, the only thing I can think of is that for some reason the reed switch I bought ( https://www.ebay.co.uk/itm/235655823756 ) isn’t compatible. Seems unlikely given I can detect the pulses?

Any further ideas?

Many thanks

Lee.

[electrofix]

you could try one long shot
try turning the tap down a bit to slow water input

what my thinking is , if your reed is not reacting quick enough it may miss some pulses.
it is a long shot and probably will fail but its free to try

after that it sounds like the board is not getting the info from the reed so it may be a board fault

Dave

[kaibart]

Yes dave could be right here as they need to work on a set water pressure I think between 0.5bar -3bar

[leenowell]

Thanks very much both. I have tried turning it down but no joy I’m afraid. Also, tried with the actual inlet hose (much lower flow rate than my hose) and still no joy. The theory seems sound to me but if the inlet hose valve keeps the water to a particular flow range then will be hard for me to reproduce that with my bypass mode? So sounds like there are a few possible causes
1. The reed switch I bought doesn’t switch quickly enough. Possible but not sure I have a way of testing this without buying the replacement part?
2. The inlet valve isn’t delivering water in the right flow range and I can’t reproduce that with my bypass method either – any idea what flow range it is expecting so I can check the flow from the inlet valve/ may be able to reproduce it with a mod to my test rig.
3. The board has a problem – is it likely that I can test this?

A couple of more bits of information….
1. I have just remembered that in my earlier trouble shooting before I changed the reed switch and the dishwasher had none of my test hacks on rinse after it started filling but before the alarm went off I opened the door and poured water in and it seemed to work. Doing the same on the eco programme didn’t work.
2. I have another dishwasher which has a similar inlet valve but different electrical connector. If 2 above is the problem could I use that to conclude one way or another?

Thanks again for this. This is a true man vs machine battle 🙂

[electrofix]

pouring water in probably wont work as there is no pressure switch to detect. they do use motor current to detect water presence but its the reed switch that does most of the work

the flow is not massively critical as the unit has to be able to work in various flow rates, was only thinking the replacemant was misplaced or not switching fast enough

Dave

[leenowell]

Hi Dave

Quick update. I bought a new reed switch from Bosch in case that is what the issue was but no joy.

Current setup
– Correct filling hose connected,
– float switch taken out but still connected

The odd thing is that sometimes the first fill works ok but then the second one doesn’t. Other times the first fill fails. Anecdotally it differs between a rinse program and a wash although need to do more tests to prove this if needed.

I have also noticed the following
1. When it errors, I hold the reset button down but it doesn’t actually clear the error / reset the program. I need press the off button off and on and then it resets. Is that normal?
2. Looking online it seems to say that post reset, it is supposed to activate the drain pump. Mine doesn’t. It only does this when the program starts and then doesn’t fully drain it.
3. I would have thought it would drain any remaining water, then fill with fresh. It seems to drain them drain some more then pause then fill .

I wonder if with my various messing around the program has got confused and the reset isn’t working. Is there a way of doing a full reset?

Many thanks
​​​​​​Lee.

[electrofix]

well we start getting into possibles now

my next guess is the wash pump. they are not cheap athough not massively expensive. problem lies in we wont know till we try one and that way of fault finding can get expensive and still fail

not sure if you have removed and checked the wash pump. you can check the pump for blockages and wear in the motor shaft. (see if it moves side to side )

the motor as a lot of dishwashers these days use the motor as a sensor. they sense motor current to determine fill level. A similar thing happens with the drain pump where motor current is used to determine if the unit is empty

Dave

[leenowell]

Thanks Dave. Should holding the reset button down clear the tap symbol error without the need to turn it off and on?

[electrofix]

short answer dont know

I assume once it goes into fault mode it need a power off to reset as a lot of machines do

Dave

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