Recently, I had a chronic problem with high pressure my Hayward DE 3620 filter. Back washed constantly, clean the filter grids thoroughly still the high pressure returned in a short period of time.
Finally, after much frustration and research I found out that the life expectancy of the filter manifold and the grids is about 5 to 6 years. If you're having chronic issues with high pressure in your DE filter and back washing doesn't solve the problem. Think about replacing the internal filter system. It's about $400.00 between the filter grids and @the top manifold, but worth the aggravation and the danger of high pressure building up on your filter system.