chris French wrote:

Removed a rad for redecorating. It's been loose for ages as a couple of
the fixing screws have come loose in their holes. Presumably I got a
joint when fixing it originally, also the plaster around the hole has
crumbled a bit.

I maybe able to relocate the hole a bit by moving the bracket slightly,
but I don't want to move the rad itself. I have used the expoy putty
before for plugging such a hole, but not sure it will work so well in
this situation, ditto for hammering bit's of wood in

Any other suggestions for getting a better fixing - the wall is being
skimmed as well.

Fill the holes with car body filler, then skim and re-drill for plugs.

You should gouge out any loose stuff and if clever, where the new
fixings are going, and if extremely clever, insert new plugs into body
filler as it sets.