chugging radiators - anyone with plumbing/ heating knowledge please help!

[Helencassi]

Hi, I'm moving house on Friday and radiators are playing up.. I don't really want to spend money on a professional to come round right now.. can anyone help?
Gas boiler is a few years old and seems to be working fine. A couple of the radiators sometimes make a loud sound like an engine chugging. When I turn down the heat dial from 4 to 3 they stop.
There is a video of the problem here : drive.google.com/open?id=1ZthAUwMWc7kpkUNL8NKIupjopHoa1-ON

it's because you have thermostatic radiator valves fitted on the wrong end of the radiator. When the room approaches temperature, it pushes the tap washer down towards its seat, but the water flow is pushing in the same direction, so pushes it down too far, and it bounces to and fro.

On the other end of the radiator, you will find a lockshield valve, which is intended to regulate the flow of water through the radiator. Take off its protective cap, wind it down to fully closed, then open half a turn only.

Leave the heating running for half an hour, with the TRV turned to max. Is the top of the radiator as hot as the others, and the bottom somewhat less hot? If so, you've fixed it.

If not fixed, report back with your findings.

We had this, our thermostat was on the correct side but the heating engineer said that there had been a dodgy batch of thermostats, replaced it with a different brand for nothing and it was fine. He's been servicing our very old boiler for around 25 years so we trust his opinion.

thank you so much Piglet John - that has worked. I am so glad there was a simple solution!