wes mine does it all the time!when i turn it off on my pole tap it alternates between the pressure ive set it at(60) and PS but then starts again when i turn the tap back on.this is normal i think.
are you saying the pump will not start up again when you turn it off at the tap when pump still running?
try setting the calibration higher.that should sort it!

if the pump is just constantly flashing PS and not working at all check the connections and wiring!!
hope this helps
dazmond