Turning the pump speed down will not help, did you try bleeding the pump?
Maily the common place to get the air lock is in the heatexchanger, not simple to remove, takes a bit of messing.
Make sure the cap on the auto-bleed vent in the boiler is open (for a while) turn the screw on the front of the pump most way open to get air out of pump (you'll get a little bleed of water there too so have a small towel in place not to get water on any of the electrics in the boiler.
Make sure your system water pressure is correct, bleed all rads and try remove all air anywhere you find.
T
March 2008
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