Water filling on Bendix DH090

Hi, I have what seems to be a common problem with the water not filling at the start of the wash cycle. It appears to be a blockage not releasing the overflow interlock. However I have cleaned the inline filters, the 2 syphon pipes and other parts of the air chamber, have removed and checked the 2 small flexible pipes from under the sump, and cleaned inside the spigots that connect them to the sump (I did get some black gunge out of the lh one). I have also lightly blown down the pipe connecting the pressure switch- which I can hear switching over. On reassembly, the machine works correctly and completes the cycle. If I then within a few minutes start a new wash cycle it will work correctly and this pattern will continue. If however I wait until the next day (machine cooled down?) the fault reappears and remains until I remove the flexible pipe under the sump. Please advise