[slief]

F8 means Air Obstruction. This is often caused by salt creep in the venturi port where the silicone air hose connects to the nozzle on the pump. It can also be caused by a dirty foam filter in the silencer as well as a pinched air hose. A snail inside the skimmer pump can also cause it because it too can obstruct the airflow.

The nozzle on these pumps is designed to pop off the pump without removing the pump so that is the first thing I would check. That said, depending on the last time you broke the pump down, it might not be a bad ideal to remove the pump, take it completely apart by removing the impeller. Set any o-rings aside and the motor, volute and impelller a 5-10 minute soak in distilled white vinegar followed by a good scrubbing inside and out. Then rinse and reassemble.

This thread discusses the salt creep in the nozzle as well as general cleaning of the RD3. I clean my pump every 3-4 months and it always looks like new inside and out when I am done.
http://www.reefcentral.com/forums/sh....php?t=2573406