RO System problems...

["John W. Lemons III" <john at johnlemons_com>]

I have a 3 stage 100gpd RO system that is begining to give me trouble.  I
recently replaced the sediment filter, carbon block, and RO membrane in the
system.  Huge improvement in quality, as I think I let it go too long.  Any
way, I noticed that the system never shuts down.  Water is always coming out
the waste tube.  (This could have been a problem for a while, and I'm just
now noticing it)  I checked that the flow restrictor on the RO outflow tube
was still in place, and it is.  I took off the auto-shutoff to test it, and
it appears to work fine, in that once I increase pressure on the RO side, it
shuts off the tap water side.  I don't know how much pressure, so that could
still be a problem.  I might measure that next.  I also checked the check
valve and it only permits water to go one way.  I'm stumped.  My instincts
tell me its the auto-shutoff valve requiring more pressure than the the flow
restrictor is allowing to build up, but I hate to just go willy nilly buying
parts I might not need.  Any experts out there care to take a shot at it?