The RXD1500 is a modified 5000 ProFlo valve by Fleck. it is a great system and should last for many years. How old is the control valve? Brine draw issues are usually either worn internals, or a clogged drain line. There can be many more causes, but start with these. If you put the system in brine draw and remove the brine line from the valve, you should here and feel suction. If you have suction for 5 minutes, that would indicate a problem in the brine line or tank. A simple loose fitting or jammed brine valve safety float can be the problem. Check the drain water, make sure it is free flowing and the drain line is unobstructed, no kinks, etc. Start with those basics and let us know what you find.