Remove the red jets from under the water tank, blow them clear. Check if water will work without the jets, if OK replace jets n job done, if no the soap pipe has grit type bits in it which have to be cleared out. First tape the trigger open, I extended the soap pipe with a piece of windscreen washer pipe for ease and sucked clear water through (be careful it tastes yukky if you get it wrong). then flushed through a full tank of hot water before refitting the jets. Always rinse the detergent from the system after use to prevent it happening again.
Rufus T, February 2010