My Delonghi Magnifica 3400 has a problme with the front access door popping open when power up, brewing and powering down. Are there any suggested fixes for this issue? Also, is there anyway to make the brew temperature hotter?

My Delonghi Magnifica door was popping open too when the machine would cycle on or off. I found that the shoot on the inside of the door was stuck. This chute is spring loaded. The chute guides the coffee from the diffuser to the dispenser ports. I think it must have been coffee build up on the back side of the chute making it stick. So when the diffuser passed by during cycling the chute would not move out of the way. This makes the door pop open. I cleaned the chute so that it moves freely and no more trouble.

If the diffusor isn't suffering from built-up coffee grinds (in which case give it a good cleaning first), then check the backplane that holds the diffusor: it has two hex head screws that have probably come loose. Remove the diffusor to expose the screws, tighten them down, and the problem should be fixed. Total repair time should be under 30 seconds.

That was happening on my machine and I discovered that there was some dried coffee grinds preventing the drip tray from being fully inserted. It was hard to see with overhead light but easy to see with a flashlight. I used a kitchen knife to scrape it out and vacuumed it up. After that the door closed fine and would not pop open.

There is only a small amount of resistance on the access door hooks. Even on a new machine you can pull the door open without using the "unlatch" tab. Don't know of a fix other than wedging a small shim along side the door, not very professional.
The temp of your pull can be adjusted through the menu. Set up is in the manual.