Bosch SS66A02GB Inconsistent Filling

We have a Bosch SS66A02 dishwasher which appears to be suffering from water starvation after the first fill in a cycle.

For the first fill it usually fills normally (to bottom of salt lid – fill process uses whole of fill matrix), but for the subsequent fills, little water is added and there is insufficient to make the spray arms turn. Adding water manually solves the problem.

On the first cycle the fill matrix fills to the top. On subsequent cycles, the water level gets no more than an inch or so into the main body of the matrix. By first cycle I mean first cycle after the machine has sat idle for a while, rather than always on the first cycle of a wash. If you run several rinse cycles for testing, the first will fill completely, but subsequent ones stall early in the fill.

I’ve done the following

1. cleaned the large hose at the front left (not much in there)

2. cleaned the large internal hose from back of fill matrix at fill matrix end (not much in there either)

3. Checked flow rate from inlet valve (quite constant over a number of cycles – not measured accurately – was 1 jug (approx 2l I guess) / 30 seconds.

4. Checked for anything jamming the sump pump impeller.

5. Cleaned out the black based housing under the fill matrix into which the air pressure sensor plugs and which from a large hose runs off.

6. Run a Finnish Dishwasher cleaner cycle through at 70 degrees

7. Removed the fill matrix and tried to clean this through. This is all clear except for a chamber at the very top rear of the machine which appears to be fed by a narrow channel up the end of the matrix at the back of the machine. This is still quite black, though can’t tell if it’s actually constricted. Had a go at cleaning it out with many cycles of boiling water. Not much came out, but the flow of buddles in there does seem more predictable now.

I’ve observed that the pressure sensor (I presume that’s what it is – diaphram mounted vertically driving a microswitch) is stopping the fill from completing properly. It doesn’t seem to reset itself when the machine empties – so you can start a cycle with it still engaged. The mechanism itself seems perfectly OK when operated outside the machine. Could there be something blocking the air path? Is that area of black matrix an issue to worry about. I haven’t had time to figure out what chamber does what.

Many thanks in advance.

Andy