Rain Soft acid neutralizer tank

We have lost water pressure from our neutralizer tank. Showers only trickle water. When we by-pass the tank, the pressure is fine. Is this a common problem with a neutralizer tank? The tank is about 14 years old. Rainsoft has come out to replace the o-rings on the by-pass as we had not been using it for at least 6 years. They want to charge us to come out and trouble shoot the problem.
Thanks, Mark