We changed the sand in our Hayward filter and used the recommended sand. We were careful when removing and adding sand and replacing the valve as we put it back together. I back washed for about 5 minutes and ran on rinse for a minute. Everything does great for 5 to 15 minutes then the water flow stops but pump continues to run. I can turn it off and it will start working again. We are just opening up our pool and since sand hasn't been replaced we decided to do it this year. Any ideas. Thanks