water marks on ceiling - now do I know where it's coming from?

[OttiliaVonBCup]

It seems fresh, but dry now.
We recently changed and bled a radiator just on top where the leak is and also have a bay window roof - again where the leak.
How can I find out what is causing the leak?
Could it be a delayed one seeping from when the radiator was being bled? It was three weeks ago, on the other hand we haven't had much rain yesterday.
What can I do?

Did a lot of water come out of the radiator when it was being bled? would it be enough to cause a damp patch to come through the floor?
could your radiator or pipes have a leak somewhere else?
There are damp companies you can call out to locate leaks.

I don't know.
I paid someone to do it...
I think it's the roof.
If the pipe had a leak it would still be leaking. It's dry now.
Bugger.