How to unblock a cornet?

Answer 1

Make sure it is not the valves, a valve(s) may have been put in backwards. Disassemble the instrument and use air pressure to locate the blockage. Use a wooden stick and air pressure to push blockage out. If this does not work, let the part sit in hot water to help free the blockage. If this does not work, either have a pro look at it or have someone you trust look at it (for a different perspective).