Its not building up pressure....because the Non return valve...is boogered....when the motor is running..it drives the flywheel, that in turn..makes the piston go up and down....the compressed air then flows into the tank..through a non return valve...if said valve is broken ..then no pressure is built up..and any air that is produced flows out of the tank...its a simple fix...if you are keeping it....value wise...on this side of the pond.....minimal... .as in scrap.....