alright techs here's one. 200h machine. 500 flow everything ok, no alarms. 800 flow cond falls, although i am getting 800 flow output from drain. everything calibrated perfect. i am thinking cfs #10. what do you guys think.

Sounds like BC Membranes or a leaky BC valve

I'd go with the bc diaphragms, if the condo falls approximately 0.5 it's just about a given, if eq. has in excess of 15k hours change them. just make sure you mark the bc housing so everything lines up when you go to put it back

Replace CFS#10 if you determine the balance chamber is not switching in a timely fashion. At 800 flow it should switch q/2.25secs. At 500 flow it should switch q/3.6secs. You can time it w/a stop watch. Since the flow rate is software controlled on the 2008H,there is no adjustment. The Actuator board controls and monitors balance chamber switching. The Act. bd also controls the deareation motor speed. So the problem you describe may be a faulty act bd. What does the temp do at 800 flow? You may also notice a cond decrease along with a lower temp. The current UL heater has 2 parallel heating elements. With both elements intact the total resistance should be between 9-11 ohms,if one element is open the resistance will be 22 ohms. So you may have a machine that is up and stable at 500 flow, but at 800 will not be able to keep up, therefore affecting temp and conductivity.