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Bosch washer dryer - trips RCD when drying

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I have a Bosch WKD28351GB which is 4 years old, I've only ever used it for washing but tried to use it for (gentle) drying for the first time. 

The machine ran for about 5 minutes and then tripped the RCD, resetting the RCD was not possible without unplugging the machine.

After leaving it unplugged for an hour or so, I tried again and it did not trip the RCD.  So I tried running the dryer again but the same happened i.e. after 5 minutes of running the RCD tripped.

After some googling I read about the mains filter capacitor and since taking the lid off I did notice that this was the area which got quite warm whilst the lid was on.

I have 20 years experience of electronic design and have worked on projects more complicated than washing machines so I'm fairly confident and capable, but I have no experience of washer dryers and cannot find a service manual.

Whats the best way to diagnose the fault and what could the potential fault be ?

Does it sound like its the filter cap and shall I disconnect it to see if it stops the RCD from tripping (I'll obviously replace which ever component is faulty).

Is this a common fault with these machines ?

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Hello. The mains filter would never only trip the electrics 5 mins into the drying cycle. If it only trips on the drying cycle it must be something that is only in play during the drying cycle and not the wash cycle. 

The main suspect has to be the heating element but It could be something else, especially as it takes 5 mins or so. Unfortunately though, unless you can see anything obvious you need an insulation test meter to diagnose this type of fault. Without one you are unable to see what is causing it to trip as described here washing machine tripping electrics

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Yep I disconnected the capacitor and it still tripped after a few minutes.  

I can feel the heating element getting hot so its obviously heating up, so why would it cause a trip during the heating up phase ?

I might be able to borrow a insulation test meter from work (I've used them before).

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It could be physically broken and expands and touches the casing when hot. You could try having a look at it. If it looks ok you’d need the insulation test meter. 

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Well it looks like Ive found the problem...

There is lots of powder (some wet) in the heating element and it appears to have come from the fan !

I assume that fan is for the dryer which has never been used, so what is the powder and where has it come from ?

I use Fairy non-bio pods and lenor conditioner, not washing powder.

If I clean it will it fix the problem and how do I stop it happening again ?

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Aye it could do with cleaning up. But I can’t see anything wrong with the heating element, so I can’t see how tripping the electrics would be accounted for. As bad as it looks I doubt it would stop the dryer from working.
 

To find the cause of tripping the electrics you’d need to find a bare wire or corroded element. If nothing can be seen you need to test each component with an insulation meter putting 500v DC through each terminal and see if any of it leaks to earth, or the metal part of the component. 
 

If the fan wasn’t running it would not dry laundry and overheat and cut out but not trip the electrics. The detergent must have gone up the top of the door seal as steam and condensed leaving the detergent. There is an opening at the top of the door seal where the dryer fan blows hot air into the drum.


 

 


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Thanks Andy

I disassembled the heating element and fan and gave it a good clean.

Put it all back together and turned it on - this time the fan worked (it didnt work before) so I thought I had fixed it.

But then after a few minutes the RCD tripped again so I guess there is an earth leakage fault with either the heating element or the motor ?

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I assume the washer will still work as the fault is with the dryer components (element or motor) ?

The machine is still in the drying programme when powered up, is there a way to reset the programme so I can continue to use it for washing ?

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Ggggrrrrrr just tried it on a wash only cycle and after a few minutes it tripped the rcd again

So now I cant even wash anything

I tried to call an engineer out a few days ago as I was of work last week but he couldnt come until next week which is when I start a new job (which is a 30min drive away) so I can't take time off work and have no family/friends nearby who could let someone into the house

This all started when I used the dryer for the first time !

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Normally a fault on the washer dryer section does not affect the washing machine. It's possible that whatever is causing the electrics to trip has nothing to do with the dryer and it was just coincidental. This fault needs an insulation test meter to track exactly where the electricity is leaking to earth. Please let us know if you get to the bottom of it.

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Thanks Andy, strangely when I tried washing again the next day it didn’t trip the rcd. I did 2 short 30deg washes and a standard 40deg wash without the rcd tripping. I’ve not tried the dryer. So it seems temperamental and was maybe a coincidence like you said. Guess I’ll have to see how it goes, I’m not sure whether to try dryer again?

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Hi. If it's tripping at random on wash, but trips every time on dry then that's strange. If it's tripping at random on wash, and trips at random on drying cycle that is more in line with what would be expected with an intermittent tripping the electrics fault. It seems like it is tripping on both wash and dry cycle so clearly the washing machine is of little use until it is properly repaired. Intermittent tripping can be caused by either leaks running onto electrical parts or chafed wires somewhere that touch something metal during the wash cycle. The latter can be frustratingly intermittent and influenced by the weight of the laundry inside. In other words a heavy load, or a load that is a bit out of balance can cause the tub to bounce about more on spin and subsequently allow the bare wire to touch the casing.

Tripping the electrics every single time would only be caused by a chafed wire if it was constantly touching and shorting to earth, which is very unlikely, or an insulation fault on one of the components. The most common components to cause fusing or tripping of the electrics is either the washing machine heating element, or the dryers heating element, followed by suppressors, capacitors, and motors. An engineer would put his insulation test meter on the washing machine and test for a reading between live or neutral and earth. If there is one you would then have to work out where the leak is coming from. This is achieved by disconnecting suspected parts and seeing if the leak disappears. However, a more accurate method is to disconnect suspected parts and test them individually by putting one probe of the insulation test meter on the metal casing of the part and the other probe on each individual electrical connection point to check for a reading.

As the meter uses 500 V DC but the washing machine and uses 230 volts there is some leeway for small readings. I forget the exact amount that is tolerated. But usually if an insulation leak is tripping the electrics or blowing the fuse is then there is usually a direct short to earth and the needle will shoot straight over.

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