Rattling Rads

[Longhorn]

The rads on the fist flr. of my house make a rattling noise from the moment sys. starts at 4.30am to the time it shuts down. The ones on the ground flr and the 2nd (top) flr do not make the noise at all.

So far this problem has baffled four plumbers . The first plumber said it was two old rads on that floor were responsible, so we changed the rads but that wasn't it. The second plumber said it was the pump, so the pump was changed and again, it wasn't it. The next plumber was sure it was the 3 way valve, so it was replaced. This was yesterday. This morning the noise came back so the valve was not the problem.

Power flush is expensive and I want to be sure before I go for it.

Many thanks.

 

[JohnD]

have you got thermostatic radiator valves?

what happens when you open and close the rad valves?

If you grab the radiator and lean on it, does it stop rattling?

If you stand beside the boiler, does it make a noise (a) when firing (b) when flames cut out?