I have a coleman 450 spa that I rescued after Katrina. It works great except that the 3 main jets at the bottom of the spa and one on the side have no water flow. They seem to be plumbed to a 4 way fitting by one of the main jets which is very powerful. It seems to me that all the water is going through this main jet in the side and not getting through to the 4 way fitting. Would it be something to do with the air controls (which work fine for all the other jets) or am I barking up the wrong tree! I have blown compressed air through the venturi inlet on the main jet in question and I get air out of the 4 non functional jets. Can anyone help please.

If the largest of the jets you mention is a "volcano" or "diverter" jet that you can turn on/off by twisting it, try removing it, then rotate 180deg, and re-fit.

Thank you - that did it. It's easy when you know how!