Bosch Logixx Dishwasher - a few more questions....

[caulkehead]

Q1 Is the Matrix on the side meant to remain full of water - or partially / totally discharge the reservoir at any point in any of the wash cycles ?

I've watched our machine run through a couple of full wash cycles but nothing seems to happen to the water level in the reservoir part of the matrix - even when it lets in water at the start or pumps out at the end.

Q2 Where is the Aquasensor which is meant to check how dirty the water is and adjust the programme ? (Part number ?)

Thanks

 

[Sleepyhead]

Its easier if you stick to one thread.
We need the enr number to see what appliance you have.
If you post the enr number and the fd number I'll be able to look up the exact machine you have. That'll maybe help diagnose the fault.

 

[caulkehead]

Thanks Sleepyhead - sorry about running with two threads - thought the first was rather lengthy and maybe a separate short-sharp couple of related questions might prompt a resonse from anyone who perhaps wouldn't have bothered with the first thread. Anyway...info requested.... the ENr is SGS6962GB/13 and the FD is 8112 (then there's another number 440147 but I don't know whether this is relevant.) I see from the Bosch Parts web site that the water matrix is actually called a Heat Exchanger - but I still don't see what it is meant to do. And although I can identify a couple of 'sensors' on the parts listing diagram it's not clear which one would be for analysing the water consistency - I guess it must be an optical sensor ? I have ordered a water inlet valve from BHS Home Appliances Ltd so will report further in a day or so when it arrives.

 

[Sleepyhead]

As far as I remember the issue is a lack of water in this machine.
If the transfer pipe is clear then the pressure chamber would be the next item to check.

 

[caulkehead]

I removed, dismantled and cleaned the Pressure Chamber (including the Heat Exchanger and all other water fittings on this side of the machine. I also replaced one of the solenoid valves) a few days ago and have run the machine a couple of times since re-installing everything. As far as I can tell everything is doing what it's supposed to be doing and all floats and micro switches are ok. When I ran the machine completely empty of all internal fittings it seemed to go through the correct programme and timing which included an initial fill sequence followed by subsequent top-ups and the machine heated up and stayed hot right until the end of the programme when the digital display went to 0. After that though I put all the fittings back in and ran the machine with a load but it didn't seem to take on as much water at the start nor do any other top-ups and the heating phase was minimal. At the end of the programme the machine was not hot, it pumped out but the digital display stayed on 1 minute and it wouldn't end the programme. On opening the machine the contents were wet but cold and some had not washed properly.This is why I think it's a water-level problem - and maybe it's not heating properly because it knows there's not enough water in it. Hence the suspicion falling on the water inlet solenoid (Part Nr. 160725) particularly if this device is cutting off the water supply too early. What's also difficult to determine is what the machine is meant to be doing at any given moment in the programme. Can Bosch (or anyone else) provide a sequence of what functions are meant to be happening relative to the time-remaining on the digital display ?

 

[Sleepyhead]

Intermittent heating can be a dry joint at the heater relay on the pcb.
However, if there's not enough water, it won't heat.
Water level is controlled by the pressure chamber.

 

[caulkehead]

So the water inlet solenoid valve is activated at the start of the programme and water flows through the Heat Exchange matrix and down through the water regulator and into the bottom of the machine. When the water in the machine gets to a pre-determined level the incoming water is then cut off by the Pressure Chamber acting on the adjacent arm which presses on the micro-switch and presumably this sends a signal to the PCB which in turn de-activates the water inlet valve. From my observations of the filling sequence (when the machine was in confused state) the water supply cut off before the Pressure Chamber and micro-switch appeared to do anything. On the one occassion however when the programme ran normally I'm sure I saw the Pressure Chamber and micro-switch activate. So is it possible that the water inlet valve is defective and cutting the supply too early or could this indicate a fault on the programmer ? (One further point that might be of relevance - for the last couple of months before the problem arose the machine was occassionally making a 'knocking noise' which I thought was just water-hammer in the cold water inlet. Maybe it was the inlet valve trying to tell us something !)

 

[Sleepyhead]

Water hammer is a common fault of the inlet valve.
You've pretty well understood how it should work.
Take the side panel off and watch whats happening.
If you manually activate the pressure switch water should stop, release it and it should take in water again.

 

[caulkehead]

Hey !!! Progress .... well of sorts ! I've fitted the new water inlet valve although that hasn't actually fixed the problem. However...in watching what happens when the machine is first turned on I have come to the conclusion that the water inlet valve is controlled by the pressure chamber micro-switch but only indirectly. I believe that all the pressure chamber micro-switch does is to trip an electronic timer - presumably on the main PCB - and it is the timer which cuts off the water supply after about a ten second delay. If the micro-switch to the pressure chamber is pressed whilst the machine is taking in water it doesn't cut the supply - hence the theory that its done via a timer. Left to itself from a clean start the machine failed to take on sufficient water so I re-started it and this time held the pressure chamber to prevent it activating the micro-switch. I only held it for about ten seconds and then released it so in effect it allowed another ten seconds worth of water into the machine before the electronic timer cut off the supply. But this made all the difference and the machine seemed to then make all the right splishy-sploshy noises, the water level in the machine was covering the s/s perforated plate at the bottom and it heated up. Previously it had only let in enough water to partially fill the white sump and then failed to heat up properly - presumably due to the low water content. I missed the later phase in the programme when it emptied out and re-filled for the rinse cycle but again it did not appear to let in enough water. As I don't know how to overide the controller for the water inlet I simply opened the door and added half-a-bucket of warm water and... voila...away we went again and it completed the programme and finished on zero. So....methinks we have a problem with the timer which controls the water inlet. Does anyone out there know whether my hypothesis is correct and if there is an electronic timer on the main control board is this a servicable part, can it be re-programmed or replaced or am I looking at a completely new control board ?

 

[caulkehead]

UPDATE - Not now convinced this is a timer problem !! It occured to me last night that perhaps one reason the machine is not taking in enough water is because the pressure/level regulator is tripping too early. Assuming the regulator contains some sort of membrane is it possible that the membrane mayhave softened and now responds too quickly when the water level rises in the chamber below it ? I had noticed that when filling with cold water the plastic assembly below the pressure regulator and the pipe leading to the sump filled up very quickly (within about thirty seconds) and then the pressure regulator activated the micro-switch to cut off the supply. When the water in the feed pipe to the sump then found its own level there was virtually no water in it. I then checked in the machine and the level in the sump was only about three-quarters full. (The pipe to to the sump is clean as a whistle and as far as I can see there are no restrictions in the water path to the sump) As an experiment I turned down the water inlet valve so that the water supply only trickles into the machine - this allows the water time to enter the machine and the build-up in the feed pipe and the housing below the pressure regulator was much slower (it took almost five minutes to fill) and didn't back up into the housing until it was obvious that the water level in the housing was the same as in the machine - ie. covering the perforated cover over the sump. The water level in the housing continued to build up in the housing below the pressure regulator until it was about two-thirds up the container with the red float. The pressure regulator eventually responded and tripped the micro-switch but this time with a machine full of water. The wash programme then continued as normal with excellent swooshing noises from the rotating arms. Have now ordered a new Water Regulator and will report back in due course. ( Hope someone's listening to all this - or am I just talking to myself ???)

 

[caulkehead]

ANOTHER UPDATE ... SO NEAR AND YET SO FAR ...just got an e-mail from BSH Appliance Care to say that a replacement Pressure Regulator is not avilable - presumably no longer stocked or made. Have dismantled the Heat Exchange unit and all the gubbins below it once again to get a closer look at the Pressure Regulator and have decided that it's probably ok - no obvious faults and indeed there's not much can go wrong with it. So.... back to the theory that the incoming water pressure is too high causing it to back-up in the pipe to the sump. Ran yet another test with water pressure turned down and bingo - no problem. Machine filled and commenced main wash. However...with some 50 minutes remaining on the timer it seemed to execute a partial pump-out which I would expected to have been followed by a partial re-fill - but all it did was make a few clicking noises and then went into rinse mode but I could hear was the sound of the main pump trying to shift air. I opened the machine and added a couple of pints of water and it then re-commenced rinsing and finished the programme with no further problem. Question - is it the main electronic circuit board in the door which controls the water intake and could this be at fault (expensive !) - or, given the funny clicking noises, could it be a dodgy relay somewhere ? There's a couple of blocks of electrical connectors at the base of the machine behind the main motor and next to the electrical mains intake but I can't work out what these are and the diagrams on the Bosch parts web-site does not show them at all. Any ideas ?

 

[ashanti8]

Hi Caulkhead. Did you ever solve the problem. Your description EXACTLY matches my problem in Sydney and i note the thread just stopped.

 

[caulkehead]

Hi Ashanti8 ! OMG - doesn't time fly ..... and now you've gone and brought back all those turgid memories of me wasting my life trying to figure out what the hell was going wrong. My wife thought that I had completly lost the plot - she would come in and find me sitting in the kitchen with the d/w partially dis-assembled watching it run through cycle after cycle. In answer answer to your question though .... yes .... I did eventually get to the root cause of the problem ... but ended up putting it into a skip and getting a replacement. The water solenoid had indeed failed but replacing it didn't solve the problem. What I eventually discovered was that when the solenoid failed it had also taken out a chip on the main control board - there were brown burn stains on a part of the circuit board. When I found out that a new circuit board would cost around £300 (not much less than the cost of the machine) I threw £50 at a company which reckoned it could repair it. Of course it didn't work so at that point I gave up. I managed to find a near identical Bosch machine for £50 on our local Gumtree site and .... touch wood .... it's still going strong! Hope you have better luck than me and manage to fix yours.

 

[ashanti8]

G'day Caulkehead. I couldn't believe when you responded so quickly. Your description of the fault finding MATCHES EXACTLY.... EXACTLY what I have been going through. It includes the description of my partner despairing (you've lost the plot!!) when coming home finding me lying prone on the floor watching and trying to decipher what's going on.... often into the late hours...
I have had 2 repair guys (recommended by Bosch) around... the first charged me $140 for 15 mins to tell me he was wasting his time because he found a dead cockroach inside and that there are probably more around the control board. I wasn't impressed.From my deduction the machine wasn't heating the water as it used to (NTC sensor?) and not enough water coming in after the initial wash... some but not enough. I had to, like yourself put a sauce pan of water in to 'kick her in the guts' to continue the cycle.

After a couple of weeks I rang Bosch Australia to tell them the story. The first recommend repair guy I remembered actually boasted that this was the 3rd machine he had looked at that morning and had written off because of cockroach signs. Not good for Bosch as it would make me think twice about buying another machine of that brand. I asked for another reputable repair person. Another representative came a couple of days later, quizzed me about the symptoms... and then asked me what i thought it might be.... not a good sign. I opted for the NTC sensor which he had to order and came back 1 week later to install. From all the guides i had researched i knew you had to separate the base from the upper workings. He reckoned he didn't... after 1 hr of cursing ending in a tantrum (full on) he departed. (never came back never been charged) I separated the base and put in the NTC sensor.. now i had hot water... but it still wouldn't fill for the 2nd and 3rd cycle fully (still needs a pot of water)

My unit (SGS46M62AU/82) has a water matrix (heat exchanger) built in and i'm suspecting that this is where the problem lies... or that bloody pressure switch!! I'm suspecting a solenoid that lets the water from the heat exchanger into the sump is faulty.... intermittent. I can measure 240v on the terminal plugs when the solenoid should activate.. but it doesn't...occasionally.

Caulkehead... that pressure switch. On your machine did the pressure arm trigger the switch as soon as water started to enter the sump or would it wait until the water was at the correct level inside and then move to activate the micro switch? Mine activates as soon as water starts to fill the machine.

It was 42deg here 2 days ago. Picture the scene of sweat dripping down of my brow.. fogged up glasses... but determined. (or stupid)

I have done the same as you... investigated Gumtree for spare parts and I'm tempted by a 2ndhand machine, evidently still working at a good price.
I am amazed at the similarity of our stories.
Tell your wife my girl has been in her shoes. Think of her this Christmas.

Ashanti8

 

[caulkehead]

Nightmare .... before Christmas ! (That was a film wasn't it ?) Anyway - you have my sympathies. To be honest 5 years on I can't really recall the technical ins and outs of the Bosch dishwasher that was eventually consigned to the skip. Perhaps the experience was so traumatic I'm suffering PTSD. (Maybe I should sue Bosch.) Suffice to say that I've not had to touch the replacement and for that I am eternally grateful. Seriously though ... as this might be my last post on this matter I would like to take this opportunity to make a plea to Bosch and all other manufacturers of household appliances that incorporate circuit boards - at risk of stating the obvious electronics are very vulnerable and particularly so when in close proximity to high-speed mechanical components, vibration, heat and water. I suspect that the cost of manufacturing the circuit boards is minute compared to the overall cost of the machine - so why the **** do you charge so much for replacements ? It's outrageous in this day and age of sustainability to have to trash something like a dishwasher just because a component costing 10p has blown. I think that we should start a world-wide boycott of all manufacturers who do not make available at the time of purchase an itemised and priced list of all service parts. Happy Christmas !