Low pressure from steam wand

The machine was working great but the steam wand is driving me nuts now.  It is still making the thumping noise but the steam is coming out very slowly.  Sometimes there's just a trickle of water.  I tried to descale the machine and also unblock the steam wand using a needle.  Nothing helps.  Does anyone have any idea how to fix it?  The machine is out of warranty.  So, I'm hoping to fix it myself.