hammering heating

[Msophief]

In our bungalow, the oldest radiators are working fine. But the newest radiators installed 4 years ago in the extension of the house are hammering at any time of the day or night and require attention: turning the valve up usually will stop the noise. Last year only one radiator would do this, and turning it off was not a problem.
This year 3 of them are doing it randomly, and we need to turn up the heat to stop the noise.
They are located close to the boiler.
What is the problem?

 

[sime10]

Thermostatic rad valves are not bi directional which means they should be on the flow pipe.
To find which end the Flow is let the heating go cold then run around all the rads to see which end gets hot first

 

[nickso]

get someone to turn the valves on the affected radiators around. there should be an arrow on the metal body to indicate whch direction the hot water should flow

 

[Msophief]

Thank you for your replies.
Kikoman has been on the job this morning
Loud voice: water everywhere, now air in the radiator. Well it won't be a 5 minute job.
Braveheart