Quote Originally Posted by bluemoon View Post
ok cheers so that not the cause of the bumping ? then... 2 rads i bled had quite a bit of air in them so would that be the only cause you think
If bleeding them doesn’t help, one of the thermostatic valve heads maybe the problem.
If it happens again, hold the TRV on the radiator that’s making the bumping noise.
If that stops it, you may need to replace the valve head. In this case, if you buy like for like, then it will be a straight swap over without having to drain the system.