Siemens extraklasse wm14k280gb has an E21 error that will not clear.

Siemens extraklasse wm14k280gb has an E21 error that will not clear. Can you assist? Your help needed.

What I have done so far:

o Removed the coin/fluff filter and cleared it

o Removed and checked the rubber pipe from drum to drain - clear

o Removed the Hanning drain pump and checked resistance - not open circuit, pump runs

o Removed the drain piping, flushed it through

With each fix I re-tested, no joy.

Whilst I was in there I changed the brushes and sprayed contacts with contact cleaner, Blew the carbon dust away. Motor turns fine.

No matter what I do I cannot clear the E21 error which seems to be a drain fault according to the net - but why it will not clear escapes me.

o In addition I have taken out the control board and it had some black dust on a specific point around two SM diodes? and that dust appeared on both sides of the board in that location but no obvious burning and no obvious source of the dust so assuming it is carbon build up from the brushes? It simply brushed away.

Same exactly as per this video at 0:34 titled Bosch PCB Repair Update on youtube - Link can be provided.

No components seem damaged, no solder joints broken, no obvious overheating. The two SM diodes seem good having the same resistance one way and none the other. Other components look good.

The PCB is a Siemens/Bosch 668675

9000 575 229-02

ako 744115-04

prg 746457-01

ak36 EPW65309

The E21 error appears as soon as the machine is switched on and no combination of pressing the drain switch and twirling the control knob changes anything.

Is it likely to be the PCB? < - this is the real question I need to be answered.

Do need an exact replacement or will another Bosch 668675 type do? I am a dab hand at soldering so I can detach/re-attach a replacement socket to a board that does not have the remote display.

I can check the motor resistances if required.

If anyone can help. This was an expensive machine once upon a time, I have also spent a great deal of time on it, Father has died of covid-19 and I am left with a doubly-incontinent mum with severe dementia and I need this machine to operate as soon as possible!