What Banstead Stig said..
I had a plastic Karcher one, it was ****e.. bought a decent one and it was a world of difference. I think someone found a decent one on ebay for cheap that was linked in another thread on here recently...
Again assuming your using a Karcher one :-
http://www.ebay.co.uk/itm/Karcher-K-...item1e9136f2c8