Jeni,
If you've checked out all the simple and obvious possibilities and still
can't get past the first few cycles, then I suggest you "babysit" the
cycle, i.e. sit and watch every delivery to make sure all valves are
functioning properly. Usually you wont be able to get a field service tech
to do this. Once, several years ago, we had a similar problem. It turned
out that the power supply was not delivering full voltages which are
required to hold some of the valves in the open position.The way the thing
works is that a high voltage is required to open the valve, and then the
voltage is dropped to hold it in the open position. Somehow, the valve (I
can't remember which one it was) was not staying open long enough. I
replaced the power supply and that solved the problem. You will be able to
determine this rather easily just by watching. BTW, I spent a good deal of
my life watching and listening to valves open and close.