Peeling paint - I need help from people who are good at decorating!

[Snickersnack1]

I also posted in DIY but thought I’d get more traffic here.

This is a photo of the paint behind my radiator. This happened within 30 minutes of my using zinsser 123 bullseye plus primer (water based) on top of the existing paint.

This is probably the first time the room has been painted since the house was built.

Everywhere else in the wall is fine (hopefully will remain that way!) just this part behind the radiator has cracked and is curling. It’s pulling away from the plaster.

No idea why or what I’ve done wrong, can anyone make any suggestions?

(Radiator is off).

Little bump in case anyone can help?

The primer you are using has acrylic, acrylic will peal like that if there’s moisture around. Could the wall have moisture trapped. It might need drying out in which case.
If you can take the rad off and test with a moisture meter ( £30 b and q ) this might give you an indication of the issue

Of note the screws supporting the rad could be allowing moisture to break through

If your walls do have moisture issues I’d switch to a fully breathable paint like
Farrow and ball breathable or Earthborn after they are fully dried out