Chosen Solution
I have been given an iPhone 5s to try and repair that boot loops. When you hold down the home and power buttons together the screen goes red before shutting off. The screen had a crack in the top left corner, so I bought a non working 5s off eBay to use as a parts donor. However, even with the new screen fitted, (with screws in correct positions) the phone still boot loops as before. I cannot get it into recovery nor DFU mode to be able to reflash it with the 3U Tools program. I presume this has suffered a NAND failure when it was dropped? None of the water indicators have activated and the interior of the phone is in excellent condition.
Have you tried unplugging the front camera ribbon cable from the logic board and see if it boots? A faulty front camera assembly can cause red screen of death bootloop.
