hi there, an update to this, i used the car this am, fine for the 1st part of the journey, ran on petrol then switch to gas fine. on the way back though, all the lights on the LPG switch were off, no sign of life from flicking the switch.
got home and popped the bonnet, i could hear a hissing noise coming from plenum and found the when the system died the solenoids were still open and letting gas though, clicked these shut. Called tinley tech with a view of buying a new switch and filters, the helpful guy said to check the wiring through from the switch to the ECU then the emulators. after doing this i did find a bad earth, low and behold near to the one for the spot lights. sorted this and so far seems to be running ok.