Sounds like the machine is giving you the run around. Is it a Giotto or Giotto premium?
Things that come to mind for me:
1. Ditch the pump and replace it. Theyre cheap
2. If its a newer Giotto/Giotto premium, they will cut out if they think they have no water. Are you using very filtered watered or very pure spring water lacking dissolved solids? These machines look for conductivity in the water. Is there any reason why the machine may think its empty?
3. Give the the tank probes a clean
4. Is the opv operating normally? If its not, this could cause the pump to stall.
5. What chance calcium scale?
If youre in Sydney, Id be referring you to Renzo or perhaps ex ECM wizard- Peter Cairis. Also, Dave at ECA knows them inside out and upside down....
Hope this helps.