Okay so I have an H machine that has been torn through and a lot replaced to include float switch, both pump heads and brushes, deare. orfice o-rings, a couple boards and valves. Really the only thing left to replace is the bakancing chamber itself. The tricky thing about it is after changing each component, the Error will go away, we re-place the unit into operation, and a couple days to a week later it comes back. Any help would be apprciated.

Check your flow motor and make sure it is rotating counter clockwise.

Have you checked the Bezzle inside the Hydroblock?

How about the Inlet Water Pressure Regulator? I have seen some on older machines that have had the stainless steel ball in them corroded, and therefore the pressure calibration would not hold depending on the position of the ball.

the BC membranes are a possibliity (how many hours?).

CFS also might be worth looking at.

Water hose quick-connect?

some solenoid valve that only goes bad after it has been "on" for a long time: your worst nightmare. If you turn the machine off (say to replace a valve), you have to run it for hours before the problem will occur again. May just have to replace each valve, one at a time, until you find the right one.

It was valve 41 Sticking, we had replaced it with another bad valve. I guess just one of the downsides to taking over a clinic thats a mess. Thanks to everyone for the tips