Kevplumb --> The thermostats are on the nearest side to the boiler.
No idea if they are bi-directional is there anyway that I can tell.
Not sure what you mean by the bypass.
ChrisR --> Almost closed the valves right down, it stopped the noise for a while, unfortunately it has returned...
I recently moved house, as the existing boiler was in poor condition I had a new Glow Worm Condensing boiler installed.
When the heating is, occasionally there is a rattling or humming noise coming from two of the radiators. If I adjust the thermostat on the radiator slightly the rattling goes...