Bed Higher In Middle Than On Sides

[Cyahr]

My printers got a problem. I've been using this printer for about 4 months with minimal issues. Suddenly I went to print something and it didn't stick to the bed and the print wasn't smooth. After some investigation when I tried to re-level the bed, the middle is higher than the 4 sides. I upgraded to the dual z axis thinking that maybe that would fix the issue. I did not. Any ideas on what I should try next? I've checked the X axis and it appears to not be bent, the glass bed isn't warped (tried 2 different beds), the z axis rods are parallel, I've changed nozzles and bed springs but still no different result. I've run out of ideas and options as to what to do next.Printer: Ender 3 Pro completely stock other than dual z axis and glass bed. Thanks for any ideas you might have!

[Bikeracer2020]

Print a level test with something like thirteen 0.2mm thick X 30mm squares set in a grid pattern to cover the bed, see printables or thangs for a suitable STL
Look at the result to determine the low points and stick pieces or strips of aluminium tape to the bed under the glass.
Repeat until happy.
You will probably find you need more than one tape thickness in places,

[Cyahr]

I’ve tried doing bed leveler prints before but it ends up clogging the nozzle if I have the sides leveled or not sticking to the sides if I have it set to the middle depth. Would the tape make any difference if the bed itself is flat?

[Bikeracer2020]

I had a similar problem with the actual heated bed bowing upwards in the middle, holding a known metal straight edge on the bed confirmed this.
The bed was replaced under warranty, but I used the aluminium foil method until I got the replacement bed.

Can only suggest to try the bed leveling STL file but increase the 'Z' offset initially to clear the high point and observe the first layer.
Perhaps start at +0.02mm offset to start and increase it in 0.01 increments until you clear the high point and shim the low points a layer of tape at a time until the different points look to have a similar amount of squish.

It is a time consuming operation unfortunately.

'Teaching Tech' on Youtube has some good videos about first layers.

[3DPrinterMan1234]

i had the same problem but in the other way