I would try a RugDoctor brand cleaner. I've never heard of Nautavac. Rug Doctors are pretty good and can be rented at a lot of grocery stores and home improvement stores. You might even be able to use the same cleaning solution that you already bough.
The machine needs a service call. The store I used to work at would give you a different one and extend the due time. It usually happens due to being clogged by pet hair.
I agree with it being cheaper to buy your own machine -- I think ours was under $200 which was half the price they were going to charge for a couch cleaning. We have a Bissel.
How much is a rug doctor to rent? Our cat peed in our guest room last week and I don't know where it is. I can buy a groupon for a carpet cleaner to come for 60 dollars.
FWIW, we had our carpets professionally cleaned and the guy (who legitimately seemed like a good, honesty employee) said the self cleaners don't really get enough water out and aren't actually good to use on a regular basis. Considering we can do the living room and hallways for $99, it seems worthwhile to go pro. Even when we did the whole house it was under $250, including a travel charge.
FWIW, we had our carpets professionally cleaned and the guy (who legitimately seemed like a good, honesty employee) said the self cleaners don't really get enough water out and aren't actually good to use on a regular basis. Considering we can do the living room and hallways for $99, it seems worthwhile to go pro. Even when we did the whole house it was under $250, including a travel charge.
Of course professional cleaning services are going to say this.
As long as you use a clean machine, extract as much water as you can, and let the area dry THOROUGHLY, then you shouldn't have a problem. However, I have heard that using ANY kind of abrasive (i.e.: spinning brush) wet cleaner on StainMaster or other stain resistant carpet will wear away at the stain resistant coating over time. Pro cleaners don't use spinning brushes (at least none that I've ever used) so I assume this isn't a concern with using them (or as much of a concern).
For the occasional spot cleaning (cat threw up, baby exploded a pouch of applesauce on the carpet, etc) we love our Bissell home steam cleaner. I've gotten back many rental deposits thanks to that thing :-)