I have been very satisfied for 2 years. This year, one of my 2 sets has starting problems - nothing comes out of any of the drippers! The pump works, the hoses are not clogged ( at every point something comes out of the hose itself as soon as I remove the connection ), but none of the drippers let water through. I put some new ones in - they don't let water through either! Is the pressure too low? Can I increase it?