Bosch dishwasher not filling
 

Hi all

You may recall that I posted last week about our dishwasher not
filling, and how I was finding 230V on each side of the soleniod valve
when water should be entering.

My current thoughts are that one of the two following things is causing
the problem:

- The control board is bust: either the valve control traic is not
working (see near the end for some detail on this) or the CPU's ability
to switch it has been lost.

- The CPU and logic is OK, but the board isn't getting some other
signal that it relies on to turn the valve on. I've looked around at
all mechanical parts, but haven't found anything suspicious.

Does anyone have any further ideas or thoughts on which of those
scenarios is more likely and how to check/fix it? If it's likely to be
the board then I think I can get one for around £50, but would rather
put that towards a 2nd hand machine if it isn't so likely.

For those that like more detail, I have, as suggested, been looking at
the electrical connections to the valve and this is the story so far:

- The 230V side of the valve is switched from the machines power input
by a float switch, so it is energised if the machine is not 'full' of
water.

- Because of this, the programme switching on/off of the valve is
controlled on the neutral side, not the line side.

- I have been able to take a fly lead from the neutral block to the
valve, and this causes water to enter (its an awkward way to wash the
pots though!)

- All the wiring from the neutral side of the valve back to the control
PCB checks out.

- The relevant line then passes through a triac, which presumably is
switched by the CPU when it thinks its time.

- I found that if I temporarily bridge the neutral line on the PCB then
the valve lets water in, but not surprisingly never switces it off, so
the fault seems to be localised to the PCB.

- I haven't been able to check the PCB while the machine is running, as
its inaccessible.

On the off chance that the triac was blown I replaced it with one from
Maplin. Although it was a physically larger package and a 50mA rather
than 10mA device the machine continues to do exactly the same, so I'm
now guessing this wasn't the cause, although maybe it was bad and the
new one is out of tolerance.

As ever, any input appreciated.

IanC