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Hi
I have a “vintage” Bosch dishwasher with problems(!).
These problems started appearing occasionally, but now they always occur (if it helps, the eco wash was affected first, then the normal wash, then the quick).
On the normal and eco wash cycles, it runs the pre-rinse but then gets stuck before the wash cycle (detergent drawer does not open); at the end of the pre-rinse, it pumps out okay, starts filling again then the “Active” LED blinks off, then pumps out again, starts filling again, LED blinks off again and it continues in this pattern about once a minute or so (haven’t actually bothered timing it yet!) and never proceeds to the wash.
On the “Quick” cycle, the detergent drawer opens (I think there is no pre-rinse for this cycle) and the wash proceeds at the expected 35 C. Sometimes the whole cycle finishes, and sometimes it gets stuck in the pump out, start filling, LED blinks off cycle as for the normal and eco cycles.
“Pre-rinse” runs as per spec – detergent drawer doesn’t open (not supposed to), water goes in, sloshes around for a while then gets pumped out.
If I pour water into the sump, then it pumps out with no problem.
I have checked and replaced the impeller jug (the swapped-out item worked okay on testing out of the machine), checked and replaced the microswitch that actuates the pump (the swapped out item worked okay after (but not reliably before) a good dose of contact cleaner, so a new one was probably in order).
I have checked the NTC thermistor – seems okay (but I can’t find the specs for this model anywhere, so I’m guessing that because the resistance does change with temperature it’s okay) – 10C – 70kohms, 25C – 13.7k, 74C – 7.5k. The heating element has a resistance of ~24 ohms (which I guess corresponds to a rating of ~2.4kW from Ohm’s Law).
I checked the control board and re-soldered a few joints that looked dry (all at the power supply end of the board). None of the electronic components look damaged.
What else to check (and don’t say “the price of a replacement machine” – I’ve thought of that and wanted to see if it could be fixed first – I’m like that)?
Odd! Usually when this happens it is either the impellor jug or the wash motor is seized. So as a failure senario as the machine fills the impellor jug tells the pcb that tells the wash motor to switch on, if it doesn`t the machine then can carry on putting, say, 2 extra litres of water which triggers that mushroom topped anti flood device under the bottom basket which rises up = turns on the drain pump then goes down and water then comes into the machine and that cycle of events carries on. Are you sure the impellor jug has been fitted the right way around as per its direction arrow? Check the wash motor. Well aware this does not account that the machine fills on prerinse only.
“13.7k, 74C – 7.5k. The heating element has a resistance of ~24 ohms (which I guess corresponds to a rating of ~2.4kW from Ohm’s Law).” What about a heater to Earth fault? possibility there.Many thanks for this.
As a quick Q – does anyone here know off-hand what the resistance of the thermistor should be at different temps for this dishwasher? Sometimes these items can fail gradually and still give different resistances at different temperatures, just not within spec.
To your points:
Are you sure the impellor jug has been fitted the right way around as per its direction arrow?
Almost 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} sure – fitted the same way round as the old one which lasted > 10 years, and occasionally after fitting the new one it ran properly on the normal cycle. I’ll have a look this weekend (I usually mark the flow arrow with a permanent marker to make it easier to see).Check the wash motor.
It washes on the quick cycle (contents on both baskets are wet if I open the door, and are cleanish at the end of the programme), so I’d be surprised if it’s this (wouldn’t be the first time I’ve been surprised, though). I can here it sloshing around in this (and the pre-rinse cycle if I run that) when it’s not decided to go into its pump out/refill sulk…Worth my checking heater to earth fault – I’ll do that this weekend. If there’s a fault in the heater rather than just a connection issue, I think it’s time for a new machine (goes completely against the grain for me!) – the price of a replacement heater is a hefty fraction of the cost of a new machine.
As a quick Q – does anyone here know off-hand what the resistance of the thermistor should be at different temps for this dishwasher? Sorry I don`t know but I can say I never had one fail.Not Bosch info but view this Chinese Logik service manual – they print`em the kraut firms won`t give you the time of day: https://www.partmaster.co.uk/logik/dishwasher/ldw45s12/catalogue.pl?shop=logik&path=400241&model_ref=1373773&illustration_ref=2245843
on pages 18 and 19
The heater unit part number is 00491756 seemed to remember they were 89 quid but just looked it up and now it is a gob smacking £175.74 (German sense of humour) via Bosch`s web site.
The prerinse the heater is not even in the circuit so could be why the machine works normally on that programme and that is my thinking on the why it then works and the quick wash at 35 degree is the inside of the machine hot or dripping cold at the end- sounds like the latter so points to a heater part earthing fault which at a certain age was pretty common.Thanks again for this. Unfortunately the values for thermistors vary for different manufacturers/appliances – so the Logik values are probably not that helpful, except to show that they also use an NTC thermistor.
The pre-rinse doesn’t use hot water, so as you say, it’s not even in the circuit.
In the quick wash the water is warm – I said originally it was 35C, checked it yesterday and it was 24C in the middle of the cycle and at the end – probably should be closer to 35 ;-). The quick wash is taking 2.5h, which is not that quick!
£175 for a heater unit is ~1/3 the cost of a Which? best buy dishwasher – so if it’s a case of a new heater for an old dishwasher that might only last a few more years (if it can be fixed!) or more landfill, I’m afraid it will be the latter.
Hi
Checked heater to earth etc – no obvious faults there – both earth to live and earth to neutral give open circuit values on my multimeter.
TBH, if anyone here could give me the expected values for the thermistor at different temperatures I’d expect them to be different from what I have measured. Since the cooler wash appears to work okay but the hotter cycles don’t, that’s where my attention would tend to focus at this point – but if I knew the answer I wouldn’t be asking…
One thing I find incredibly frustrating is that none of the spares suppliers will provide values – they are perfectly happy to sell you the component, but if you open the packaging to test the values (and it turns out your currently installed item is in spec) then they won’t refund you for your unused purchase. If it only cost a tenner or so, I’d take the chance, but since these cost 40- 60 quid (depending on supplier, time of day, phase of the moon etc) I’m not willing to chuck my cash down the swanee on the off-chance this is the issue.
Checked heater to earth etc – no obvious faults there – both earth to live and earth to neutral give open circuit values on my multimeter. If you had a megger that might have shown it up to earth. The ordinary multimeter might have or not. so could still be the heater fault which is common and failing like it could have with the symptons you describe it is not uncommon.
As far as your question goes on the thermistor( 00165281)values no idea. Just spent hours looking on the net fror you and got zilch. Not published.
Assuming that you mean a Megger (or similar high voltage – by which I mean something ~500VAC) insulation tester and not a Megger-brand multimeter – that would give a rather more definitive answer than my cheapo Halfords multimeter! Since I can buy a fairly decent new dishwasher for about the price of a bottom-end Megger tester (the MIT310 is one I’ve seen advertised), and this would likely be a tool I would probably use once, I’m not going to be doing that test – but many thanks for the pointer (I’ve spent some time reading about high- and low-voltage testing for insulation integrity since I read your post – very educational). Sometimes I have to admit defeat in my struggle against the throwaway society…
Again, thanks for spending time trying to find out the values for the thermistor. If nothing else, it makes my more annoyed that an expert can’t get the information!
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