Bosch check water light fault model SMS40T32UK/45

[Schomosport]

Machine faulted a couple of days ago and I a have been messing about with it since trying to figure it out with the help of these forums. Its now sat outside with the LHS side panel off and jury rigged water and electrical connections which is easier than messing about in the confines of the kitchen.
I have followd it through a few aborted cycles now and here is what happens:
1) Start
2) Pump operates for a few seconds
3) Arms spin for a few seconds
4) Machine fills with water
5) Arms spin for 10 minutes, firstly fairly quietly and then more powerfully. At least thats what it sounds like.
6) Machine goes quiet. I guess it might be heating the water at this stage?
7) After about another 4 minutes a pump pulses three times in quick succesion and a small amount of water comes out of the drain house. The ‘check water’ light then illuminates and that’s as far as it will go. Total cycle time to fault 18-19 minutes.
I have:
Blown down drain hose from the outlet. I can’t, its blocked or sealed by a valve.
Pulled all the internally accessible filters out and cleaned out the gunge.
Stuck a flexible cleaning wand (old throttle cable outer) into the outlet. No joy there.
Tilted the machine 45 degrees left and right as suggested elsewhere on this forum.
I am considering replacing the timer PCB since it is often quoted as a failure point within these forums. Just winging it though.
There’s a bottle of Finish cleaner sat on the side, haven’t put it in as of yet since it needs a 65C cycle and I haven’t yet had it run far enough the cyle to get to hot water so doesn’t seem much point in putting it in.
Model is SMS40T32UK/45 and it is 50 months old. It was heading for the dump since I have never yet managed to fault find and fix a dishwashers but I don’t like the price of a new machine which will probably also fail after a similar period for a similar reason. Some £15 – £30 part fails and disables the machine entirely but I can never quit figure out wahat it is. Maybe I will have better luck this time? Thanks in advance for any suggestions that may help get it back up and running again.

[Schomosport]

Took the water matrix out today and cleaned it. Tested the reed switch on the water counter PCB. Reassembled and run it round again, all same as previous, stops with three spurts out of the drain hose. While powered on pulled the connector off the water counter PCB multiple times in quick succession. Did it twice, ecah time after a few make/breaks the machine started to fill with water for a few seconds before stopping. Guess I probably simulated the impeller wheel and fooled the controller into providing water. Out of sequence, so means nothing in terms of correct operation, but probably confirms the counter PCB and the connection to it is OK.
Unless someone reading this has a better suggestion its ALL coming apart if only for a learning exercise. Now written off, need a new one, in my head so nothing to lose.

On the blockage front, with the water matrix removed, which of the 5 ports which connect to the water matrix should I be able to blow through and which should I not because they are closed by a valve?

[electrofix]

it cant be the reed switch as your saying it fill and starts to wash
if the reed sw fails it does not get that far

is a weird fault and not one i have come across

Dave

[Schomosport]

Thanks Dave. Is there a duffer’s guide to taking the base off this model? I am not 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} convinced there isn’t a blockage somewhere but I can’t access the sump area from the LHS. I would like to be able to physically check all the pipes are clear and if there are any switches or solenoid valves in there I can then test them.

One thing I didn’t mention early was the check water light behaviour. When it failed the first time while plumbed into the kitchen the light was winking and the drainhose was hot so it had got further round the cycle than it has since it took it outside. Outside the check water light never winks. This model doesn’t have a display other than LEDS, does the unit have the capability to return fault codes by flashing or illuminating the LED lights in sequence?

[electrofix]

it does have fault codes shown by light
also the water light flashing and not flashing means different things

see the owners manual

Dave

[Schomosport]

Thanks again Dave, if in doubt RTFM.
OK checked manual.
Not flashing is all about water supply blockages and waste water pump blockages. None so far as I can see. Interestingly it says failing to lock the waste water pump cover correctly will also bring this fault. All the filter bits and the cover are sat on the bench and haven’t been replaced including the pump cover. It hadn’t occurred to me that that there might be an interlock between the pump cover and pump operation which is what the manual is implying. Would make sense to keep errant fingers out of the pump when it is operating. I will replace the cover and try again. Typically DIY fault finding attitude, why keep replacing covers you will probably have to take of again at some point.
Flashing water light is the helpfully titled ‘technical fault, call customer service’.
My expectation now is that replacing the cover will kill the non-flshing water light and then later in the cycle I will get the flashing light. We will see. The m/c has been banged about a fair bit now so if the ‘technical fault’ has arisen through bad connection somewhere it might just work now. Fingers crossed. Going on holiday on Friday so might not get around to testing again until month end but will report back in due course.

[electrofix]

” Interestingly it says failing to lock the waste water pump cover correctly will also bring this fault.”

of course it will as with the cover removed the drain time will increase if it happens at all

Dave

[Schomosport]

Update time.

Refitted all the filters and covers around the pump and tested unit. As expected constant check water light did not appear and waste water from the first (rinse?) cycle successfully pumped out. Even better, the unit completed the full cycle and shut itself down without the flashing check water light appearing. Took bull by the horns, dragged it back into the kitchen and plumbed it back in. Set it off on another cycle with a container of Finish dishwasher cleaner which it again completed. Declared unit now ‘fixed’ and it has been behaving itself for the last 10 days and hopefully somewhat longer.

The original fault (flashing check water light) occurred on one of the hot pump-out cycles because the drain hose was full of water. You could hear the pump repeatedly go through a ‘try to pump, pause, try-to-pump’ cycle. I have no conclusive answer as to why the machine faulted, but the pump action suggests a blockage somewhere in the waste pump plumbing. Cleaned it all out but didn’t find anything substantial so might have been a glitch or might have been a blockage that has been cleared with the amount of bouncing the machine got between the kitchen and garage. I had mentally written it off as scrap so wasn’t particularly gentle.

Some notes for those fault finding similar machines:

If the waste pump cover is not installed, the waste pump will cough three times at the start of the drain cycle (drain hose pulses) and the check water light will come on. There is no mechanical interlock that stops operation as I previously surmised, it appears that the cover forms the outer of the pump pressure chamber and if it is missing then the pump can’t build up any pressure and after three attempts the control system has decided it’s a fault. Probably some motor speed or current monitoring check. (As Dave has said: “with the cover removed the drain time will increase if it happens at all”.)

The water matrix on the LHS gets full of gunge. Removal of the matrix for cleaning requires pliers to remove the clip holding the flexible hose which then requires some effort to pull off, then the water inlet screen and a second smaller plug need unscrewing from inside the wash chamber on the LHS. All finger tight. And the connector to the water monitoring PCB needs disconnecting. When putting it back together locating the seal at the water inlet screen is a bit fiddly, there is no positive location. If it were a bit on a car engine I would use grease to locate it but maybe not so smart in something that washes things one eats off. Maybe butter or lard would work to help hold it in position, I managed without.

I ran it in the garage for fault finding as the kitchen was cramped; the garage also sits between the house and the car that was going to be used to take it to the dump. Used an adapter on the garden hose to get water in, there’s power in the garage and dumped the waste into a watering can and a bucket. Two containers of 10 litres is plenty and you could get away with one since there is plenty of time to empty the container between pump-out cycles. The total water used is only about 20 litres.

This machine appears to have three active cycles on the 65C wash (I stood there and watched it through the first one, take something to read if you do it, it isn’t very exciting). I think the cycles are 1) cold rinse 2) hot soapy wash 3) hot rinse and dry. The ‘drying’ indicator lights up during the rinse stage of cycle 3), no idea why. If you have the side cover off you can put your hand on the side of the washing container and feel the temperature increase. Takes quite a long time before it comes fully up to temperature. Note do look out for and avoid electrical circuits if you are doing this. Not advisable if you don’t know what you are looking for. I am a home DIY-er, not a white goods repair professional so this is commentary, not instruction or recommendation. The cable to the water monitor PCB on the water matrix is an obvious one to avoid although I suspect it is too low a voltage to be harmful.

Hopefully I will now get some more time out of this machine, thanks to Dave for his inputs and putting me back on track regarding the waste pump cover.

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