the high pitched squeeling is your pump airlocked.
turn system off, locate the pump, may be in the cupboard next to your copper cylinder. in the centre is a screw remove screw to bleed pump.then replace the screw.
on the side of pump is a speed setting, set it to the highest 3.
turn your wall heating stat up and turn boiler back on
that should release any air in system.
once system running ok switch the pump setting back to where it was, most times they are on 2.
hi-spec plumbing, July 2007