Hi theecirp...this should help.
Your valve should have integral stops...so just remove handle from valve, then remove the face plate (remove screws) and tighten slotted fittings clockwise to shut water to valve (if no integral stops may need to shut water main off to do repair).
Then there is a chrome sleeve...that just pulls forward to remove. Then you will need to unscrew the rounded chrome nut you see in the picture by turning counterclockwise...this can be hard...but will spin off.
Now, you should see a white or black plastic, serrated part on top of cartridge...NOTE POSITION OF THE PART..it is a temperature limit device so needs to be placed back exactly as you find it.
Then just give a quick wiggle/small yank to the cartridge and cartridge should slide out. The seats and springs are under there (part # RP19804 from Delta). Pull seats/springs and replace.
NOW...put towel over face of valve and have a friend just pulse the water main (or separate shutoffs) to clear the lines of any debris. Look inside for anything obvious.
Then just reassemble and hopefully good to go. Let us know how you did.
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. Thank you.