In Black Crusade's character generation it's said that the weight of a Chaos Space Marine is 500–1000 kg, depending on the armour. I have always wondered, can a Chaos Space Marine or a Space Marine remove their armour for taking a shower or even to have sex?
I have never seen a Space Marine without armour, but I have never read that it is attached to him permanently.
I have been playing Warhammer 40k for over a decade but am not a complete authority.
Yes, a Space Marine can remove his armour according to the Deathwatch core rulebook.
The Deathwatch core rulebook's armour section explains that it takes around 30 minutes to remove or put on power armour with 3 chapter serfs (slaves). In an emergency it can be done in 10 minutes with one serf, but no less than that, as the proper rites must be observed.
I ran a Deathwatch game on a ship where they were not in their armour and had to either put it on or fight without it - very fun and lots of RP opportunities.
In the third Grey Knights novel, the main character is captured by Chaos and made to fight on an arena world. His armour is taken and the book deals with him adapting to not having it. Do note that when he gets it back near the end of the book, he carries it around, refusing to wear it until it can be purified by the tech-adepts. When he is forced to wear the storm bolter gauntlet it burns his skin.
Space Marines are trained to maintain a state of readiness so would remain in their armour at all times unless there was a point to removing it such as repair.
Space Marines have many enhancements such as extra organs and equipment built into their armour to deal with anything not related to killing the emperor's enemies, such as cleaning, eating or sleeping. They can do their activities in armour, they just don't have to.
As an aside: Space Marines don't have sex - they're eunuchs. Being genetically engineered to kill, genitals aren't necessary.
TLDR:
Yes armour can be removed, check deathwatch core rulebook.
Armour is taken with weapons when captured but is very difficult to get back on in this situation.
A lot of prior discussions on this topic suggest that yes, a (non-Chaos) Space Marine can remove their armor, and when not in their armor they tend to wear robes.
For a concrete case: According to the Lexicanum, the Imperial Fists have Honour Duels in which two battle-brothers are stripped down to their torsos and a judge wears only a black robe and helmet. That would be hard if they were permanently fused with their armor.
As for Chaos Space Marines: Depending on their mutation (or the extent of it), they may be permanently fused with their armor, or they may still be free to remove it.
On page 88 of the 2nd edition book Codex Imperialis by Rick Priestley & Andy Chambers it states
Champions of the God Khorne are savage fighters whose body armour grows to be part of their bodies so they can never remove it. […] Chaos Champions of the World Eaters Space Marine Legion wear armour of this kind: it remains part of their bodies forever and cannot be removed.
There is a note at the start of this section that "Chaos Champions" will refer to Champions, Heroes and Mighty Heroes for convenience.
So, from this we can infer that Space Marines can remove there armour, and non–World Eaters (except possibly some other Space Marine legions and chapters pledged to Khorne) can remove their armour.
Now, this source is rather old, so it may have been overridden in the meantime.
While there aren't completely armorless models, there are a number of normal "bare" heads included on a number of space marine sprues, as well as chaos space marines with different naked bits (arms/tentacles). So, while there are probably a number of "hoses" and whatnots associated with the suits, and probably a number of Inter-venous hookups, the suit wouldn't be like the shell of a turtle and required to survive, more like the shells of Hermit Crabs ;) ALMOST vital, but able to be removed for maintenance etc.
The Thoursand Sons are burned into their armours. They cannot remove it as they are the armour with soul.
In the novel Storm of Iron, Kroeger the Iron Warrior Khorn berserker took off his armor & yes Space Marines can have kids. Salamanders have sex with women & they bear children.
