It may be you just need to give the needle packing screw a little tighten. (Unusual whn new but things happen) Take a long narrow screwdriver, remove your needle and trigger etc from the body of the brush, and look down it towards the nozzle. You should see a slot for the screwdriver. Even a quarter turn might do it, it shouldn't take much, and it should tighten the seal to stop paint getting back there if that is the problem. When you reassemble the brush and put the needle back in you should feel some resistance as you push it through, but not enough to stop it moving smoothly with the trigger.