Sound of water running through radiator

Recently had an extension with new boiler (Vaillant ecoMAX) installed plus a number of new rads. In order for all rads to be hot, boiler needs to be turned up to max & if it is turned down slightly different rads cool down yet some are still boiling hot. Also, tall rad in bathroom upstairs now has the sound of running water through it whenever the heating is on. Have bled rads throughout house & got clear water from all & no air.

Any advice would be appreciated.

G

Have a look at the Wiki and FAQs at the top of this forum and try Balancing.

Also check that your system is full of water at the correct pressure.