if you are feeling brave you could take the noid apart, the rod might have just got stuck, take it apart ,LIGHTLY grease it with a thin lube, not thick like dow 33 and reassemble.
If you do, be gentle and keep clean. The seals are small and mating surfaces need to be kept very clean.
Before you strip it, take it out and slowly gas up the marker. Air should be present at one of the ports below the valve, if not then go back to the lpr.
i have changed the battery i think it must be the noid or the board not sending enough power to the noid. i just need someone to lend me a noid or board to rule one of them out.
Get your 9v pp3 and a couple of wires, and pulse the valve (solenoid) with it, observing it's polarity and after dissconnecting it from the board. If you have a 6v power source use that.
right after trying the board and noid on an alias i have narrowed it down to the noid. can anyone fix these or have one for sale. pheonix and planet haven't got them and if they did they would be about £80-£100!!!
cheers tom i have got a new solonid now but i might as well send it to you and save it as a spare can you please pm me your addy and i will post it to you.