Advice on repairing this ceiling plaster crack

[john2k]

I need some advice and help please. My house was a new-build when I purchased it and it's about 10 years now. Haven't had any cracks on the plaster for a good number of years until few years ago only one area downstairs on the ceiling corner where I think two plasterboards meet with a butt joint there seems to be nasty cracks. i've attached a few photos below. One bit of the plaster if i press it i can feel and see the thin layer of plaster move so it's literally on its way and will probably eventually just fall down.

So i want some advice on what's the best way to tackle this to get a nice result without major work or without having to repaint the entire ceiling. If i break off the piece of plaster that's falling off and take it to B&Q i should be able to match a close enough white tone to that. Being on the ceiling I guess it doesn't have to be perfect match. I'm assuming I need to brake off all the loose plaster and then fill it up? what will be the best filler that's easy to work with and easy sand and apply for someone who has no plastering experience? And preferably a filler that will actually stick and wont let go after a few years of vibrations like the last one did.

Would really appreciate some advice. Thanks

Pic below:

 

[Mottie]

I’m no expert but that doesn’t look like a 'normal' ceiling crack to me. Looks like you have some movement there. I’d check that out carefully before doing any repairs.

 

[john2k]

I’m no expert but that doesn’t look like a 'normal' ceiling crack to me. Looks like you have some movement there. I’d check that out carefully before doing any repairs.

How can I determine if there is any movement? it's been like that past few years and i just thought it's down to the vibrations from top floor. Its right at the corner of the end of the room where it's open plan and I believe there must be an RSJ or something holding the top floor up all the way across. If I look carefully under certain lighting conditions i can see a butt joint hump along the entire line so I know there must be a plastboard joint exacty where its bubbling and flaking away.

 

[Why Not Indeed]

As Mottie said, that doesn't look like joins between sheets of plasterboard [they're usually dead straight]. Was the ceiling papered? What did you do to cover up the cracks last time? Trying to think of what might explain the shape of the crack.
Does it move when somebody walks about above? [get up on a chair, shine a torch across the ceiling and ask someone to move about upstairs].

 

[john2k]

As Mottie said, that doesn't look like joins between sheets of plasterboard [they're usually dead straight]. Was the ceiling papered? What did you do to cover up the cracks last time? Trying to think of what might explain the shape of the crack.
Does it move when somebody walks about above? [get up on a chair, shine a torch across the ceiling and ask someone to move about upstairs].

I'm not sure if the ceiling was papered or not. It was a brand new build just over 10 years ago. I never covered up the cracks. I will try method of someone walking above but just above that area is the edge of the building. I will try in the morning to walk above it and see but its very loose plaster that would have fallen off if there was vibrations because if i just tap it it's very hollow. Below are some more pics: