Mitch, I dont know about your machine but on mine there is an in line filter between the water block and the solution pump. If this blocks up you will have no or very little pressure.
Also somewhere you may have a hole in the line. But this wouldnt stop the flow entirely, just weaken it so to speak.
On mine I have a 3 way valve but on yours I think it is a two way valve. Anyway, if this valve has decided to become a one way valve then of course only one side of it will work. They are not worth messing with, thats if you can, so I would just replace it. Doesnt hurt even if thats not the issue.
Depending on which or what chemicals you are using one of the internal solution hoses might just be blocked. It is more likely for it to be the male end fitting that is blocked and not the actual hose.
What you can do as well is to just keep taking a hose off untill you find the culprit. Then of course just replace it. Mine all have q/d's on so it is easy for me to do as I have suggested. Having said that the high pressure hoses arent q/d they are male/male for female to female adapter making it simple to work on the machine. If ths is the first tme you are working on the machine you might want to change to what I have done as it makes on site getting out of trouble only 5 mins work instead of a couple of hours or worse having to go home to sort it out.
Other than that give me a bell and maybe there is something else I can think of.
Best, Dave.
P.S. There are many other places that could have filters so check them too.