Bosch WFL 12440 GB washing machine - no heat

[Jon345363635]

I noticed that this machine had stopped washing properly and after testing I could see that the heater wasn't working. This doesn't interrupt the cycle, though - goes through the complete wash and stops as normal - sounds really nice from start to finish. Just doesn't heat the water and this obviously is the reason the drum is starting to smell.

I have tested the element with a meter and got a reading in ohms so that isn't open circuit, at least. But when I connect the meter to the wires that connect to the heater (after disconnecting them from the heater), to check for voltage, it always reads zero. At the time when I would expect there to be a voltage present, the minus (-) symbol does appear on the meter display, but no voltage.

I'm not sure what to check for next! Maybe something on the main board at the top of the machine? Would there be a component there that would be blown? Is power supplied to the heater through a relay that could have dirty contacts? I see a few of them on the board but I don't know. I can't find much info, so any help would be appreciated. If I could see a schematic it might help, but I can't find one.

 

[zipper]

There are only so many causes of a no-heat problem. If the element measures around 25 ohms then it's ok.
You should check the heater circuit wiring & the NTC resistance (cold & hot). It should measure around 6 kohm at room temp, dropping to ca: 500 ohms at 85C.
If the above check out ok then in all likelihood your pcb is history (heater relay shot or track/solder point blown). It isn't possible to "repair" relays.

 

[Jon345363635]

Thanks for the reply. I am just in the process of tracing the wires for the heater to see where they connect, so I'll test it out as far as possible and hope that I come across a break in the circuit somewhere. With a lengtch of wire attached to one of the heater element wires, and the meter attached to that up at the top, I should be able to check continuity through the board. I did look at the board and didn't see any breaks or dry joints anywhere so maybe a relay contact has failed.

I just thought there might be a well known problem on this model which causes these symptoms, and which can easily be fixed, but apparently not so I'll keep testing through the circuit and see what I come up with. I couldn't see a thermister but it's probably on the board somewhere - need to expose it fully to have a look.

Thanks again.

 

[zipper]

The NTC is on the heater, it has a plug with 2 thin wires to it. If yours doesn't have one on the heater then its mounted in the back of the tub. But most likely the pcb is goosed. Post the full "E-number" on the door sticker if you need model specific info.

 

[Jon345363635]

OK, that reads 5.6 on my crappy little meter on the 200k scale but it doesn't heat up so that's the only reading I can get.

Now that I can access the terminals properly, I get .024 on the 2k scale across the element.


The label reads: E NR. WFL12440GB/05 FD 8409 700504

 

[zipper]

Put your meter on 1 x ohms to check the element (24 ohms is ok). The NTC has to be removed & popped into hot water to check it, but I wouldn't bother if it reads 5 - 6 kohm cold. Unless you find a broken wire you need a pcb

 

[Jon345363635]

I'm hoping it's a relay - I'll see what readings I get there but if it is a relay and I can't replace it I guess I'll have to locate a board.

 

[Jon345363635]

OK, I got the circuit board removed and separated the two halves of its plastic cover so now I can see inside.

I see a small transformer with a diode on either side and they're both covered in soot, as is much of the board. Looks and feels like carbon from the brushes but isn't that a long way for it to travel and get inside there?

I'm thinking something on that board is blown although there's nothing to see other than patches of soot so I'm cleaning that off and will test the components. Luckily it will be one or both of those diodes and nothing more. Here's hoping...

 

[zipper]

Pcb components (& especially components that generate heat) attract expended carbon dust from the motor brushes.
This is entirely normal & not a conclusive sign of failure. A failed heater relay may show no external signs of failure.

 

[Jon345363635]

Thanks - that explains that.

But I think I've gone as far as I can for now - I have hooked up another machine for now, albeit one that works when it wants to, but that's another story. At least it will give me time over the weekend to really examine the board properly while running so I can check what's going on with those relays.

But if I can't find anything, I can't see what else it could be other than that board, so I'll see if I can get a replacement.

Thanks again for your input.

 

[zipper]

http://www.emwelec.co.uk/

 

[Jon345363635]

Great, thanks - might be needing that!

 

[Jon345363635]

I replaced the sensor but no joy. When I measure the voltage going to the heater element wires (while disconnected from the element), I get about 32 volts. Any ideas what on the main board would cause this. I assume it is a mains voltage heater so the 32 volts should be 240.

Any help would be greatfully received.