A simple question i hope....

I've got really bad flow through the fuel cooler radiator - I mean really bad. Mains pressure water in results in not more than a dribble coming out.

I've tried normal flush solution and I've risked exploding it by power flushing it but nothing nasty comes out

Can anyone confirm this radiator is normally free flowing ? and if it is any drastic solutions that might shift whatever is clogging it .

Thanks in advance