I inherited an inground pool when I bought the house 3 years ago and everything worked okay even though it has pretty dated equipment like a Jacuzzi Laser 225 sand filter and an old Hayward Superpump. Due to various personal reasons, I only got to open my inground pool this past weekend. I was glad that it was not a green mess but it was dirty inside - probably due to the powerwashing of the deck a few weeks ago.
Anyway, I connected everything, started it up and vacuumed the pool. When the psi increased, I tried backwashing it and for some reason, only a small flow of water flowed out (the water in the sight glass hardly moved at all). I tried switching it to drain and the same thing happened. When set it to rinse, it also appeared to be on low pressure. However, when I switch it back to filter, it works fine.
My initial conclusion is that the sand could be old and clogged where the backwash/drain pipe is, so I am thinking of replacing the sand as I suspect the sand has never been changed for decades. Let me know if I'm on the right track or if there is something else I should check before replacing the sand because it is going to be the pain to disconnect the pipes seeing the way they have been connected to the sand filter.