This indicates a problem with the non-return valve pip not sealing, the non-return valve assembly not sealing correctly into the bottom of the pump tube, or less commonly but more problematic, a split in the pump tube. Pumping then immersing in water should give clues.
Got air bubbles coming out of the plunger I put the original pip in the nrv still the same I put a lead washer on it which made it leak faster I stretched the nrv spring tightened everything as tight as I could but still leaking.
The common problem I have with the pip is getting it level against the seal surface. Replace the pip and test or dunk test till it passes. Clean burrs from all NRV parts. Ensure the spring moves freely each time.
That's the end of that unfortunately the bloody nrv as snapped and took away the threads in the tank tube and dropped inside the tank. Cheers for all your help we did get it going if only for a short period. Best I stick to my Coleman's in future.
Have a close look at everything. You say there was no lead washer fitted to the stove when you got it, double check just to make sure. The new washer needs clean surfaces to seal against, any remains of an old washer may prevent this, you shouldn't need to put huge tightening force on it to get a good seal.
