What is a cell (easy description)

The gameworld is divided into small cells, which are loaded when the player is near. With the console you can go to those cells, for example:
coc redrocketext will bring you to the Red Rocket near Sanctuary.


What is a cell reset?

A cell reset means, that every item and enemy that has a respawn flag, will respawn in the cell. The cell reset is different from Skyrim and only god knows how it does really work. Setting it to 1 hour and go to sleep will not always have the effect to reset the cells, but there is hope, if you read on.


Force a cell reset

Go to your Fallout 4 folder, where the exe is located and create two text files.

First file:
setRespawn.txt
Open it and paste:
setgs iHoursToRespawncell 1 
setgs iHoursToRespawncellCleared 1
set timescale to 99999
pcb

Second file:
resetRespawn.txt
Open it and paste:
setgs iHoursToRespawncell 168
setgs iHoursToRespawncellCleared 480 
set timescale to 20

Save and close.

-- Notice, this will drain your thirst, hunger and fatigue --
1. Go ingame, go to an interior of your choice and open the console. 
2. Type: bat setRespawn
3. Close console and after 1 second reopen the console.
4. Type: bat resetRespawn
5. Close console, leave interior, everything is resetted.

Side effect you may see, is a blue landscape in the distance. Nothing to worry about. Just save your game and restart Fallout 4.


Known bugs 

Cell resets do not work correctly. There is a bug, which causes the cells to respawn after minutes, when leaving the cell.
This bug is now fixed with Buffout 4 at Fallout 4 Nexus - Mods and community (nexusmods.com)