Carpet washer - partially working (Harwell OX11)

Vax carpet washer - been in storage for about 2 years. When put away, it wasnt working very well. It will wash the carpet (dispenses the water/solution fine, carpet beater brush works), but it wont suck up the dirty wter properly, it only pulls up a little bit. It could be gummed up with cat hair somewhere. Family.member has had a go fixing in the past and got it running but its now broken again. There is a spare drive belt for it. Anyone want to have a go fixing it before it goes to the tip?