Newbie with solar panel question/problem

Hi y'all.
Just started up my pool, cleaned everything out and turned on my solar panels. The pool filter PSI jumped up from 12 to 33 with what seems to be very little water making it through the solar panels.
Could I have blocked panels? Can they be backwashed?
Could it be a faulty valve?
Called the company who instaled them and they seem to be very vague with no real answer. They have to come out and have a look ($$$$)
If they are somehow blocked, it could have started a little last year as I noticed that the PSI was increasing a little (up to 30) with a dirty filter.
Thanks for your input:)

21 psi seems like a high delta to me. Most solar panels should add < 10 psi to the normal PSI. What was the delta after they were put in?

Since the solar is post filter, it seems unlikely to have anything that would block all or most of the panels at once. It could be the valve but I don't see how that could fail in only the solar direction.

If it is post filter, and if he has a sand filter that is failing, it could be putting sand into the solar panels. Maybe try flushing it, you could remove it from the pool, lay it flat and run a hose through it and see if it comes through clean.
When our pump hoses would get sand in them, the only way to get it out was to pump clean water through them. (Pump hoses, as in pumping ground water with construction pumps)

The filter is a DE. I can't see how DE would or could block solar panels but I am no expert. Thanks for all yor feedback so far.

Sorry. What do you mean by delta?

Delta is the difference between PSI readings with and without solar. 33-12 = 21 psi delta

Thanks Mark.
The Delta was about 8 when the panels where put in.

8 PSI sounds about right so you definitely has some blockage now. I don't think there is an easy solution to unblock them other than take them apart and clean the headers out. Unless you feel up to it, your installers are probably your best bet.

Most solar systems have bypass valves that leak (they are designed that way). I hate to ask, but are you SURE that these valves are fully open? If they were closed, they would still allow a little water to flow into the solar, but would create a huge pressue delta.

Or, is your 3-way actuator valve possibly getting stuck halfway open (sending only a little water through the solar but creating one heck of a bottle neck in your system)?

The valve turns all the way to open. Could be that something is not working properly insde?
Could DE block the panels? Can DE get passed the filter?
I appreciate all your help.