[QUOTE=Discocom;7412860]Many thanks for all the advice. I wonder if the cylinder was slightly overfilled, which caused the problem as working fine now.



Sorry I was a bit terse there.

An overfill can give the hammer too much pressure to overcome causing failure to fire.
Check the weight of the cylinder,usually indicated on the side.
On my FWB you can let a bit of co2 out if you have overfilled.