Opening a DE filter


Active member
Aug 25, 2015
ny ny
So this may have been a bold attempt but no good deed goes unpunished....

I figured out how to close/open my own sand filter pool no problem and have been doing it for years..

However my aunt decided to have me come by and do her DE filter pool which I gave her the disclaimer that I might miss an extra step.

When I closed it last year I blew the lines out no problem, unhooked the pump and had the water drain out.

What I couldn't find at the time due to limited research was the drain plug on the actual filter unit (Pentair fnsp 48). So there may (probably) have been water in there all winter...oops.

How much damage control should I be expecting if I left water in there all winter? and for opening a DE filter pool should I be expecting to open the filter and examine all the grids/manifold?

Thanks, and hopefully I wont be posting another thread for any other problems...
May 9, 2017
Galloway, NJ
The drain on that filter is on the bottom under the inlet/outlet connections - it can be a pain to get to. Some people use the backwash setting to drain most of the water. If you had water in the filter and/or the control valve and it froze you may have a problem - anything from a cracked tank, valve or damaged DE grids. But since you didn't drain it you also probably didn't clean it - that needs to be done. You can find a manual online. You have to pull the top off the tank. It's possible to clean with the grids in place with patience and a hose, but I always pull mine out. When you clean it you can look for cracks in the tank, the DE grid manifold or damage to the grids. If they or the manifold are damaged you'll pump DE back into the pool. Once you've cleaned it you can reassemble and test for leaks. Hope you have no damage.