Check the water level in the big header tank in the loft, it may be low, you can usually adjust the ball cock up to allow a greater volume of water in the tank, but not to much, try to get the water level about 50mm below the over flow/waring pipe. If it is airlocks, then there may be a problem with the hot water pipe coming out from the top of the cylinder, it should rises up or have a kink in it of about 450mm. Also check out any other pipework that was renewed when you had the new boiler install, if there is any high parts where air could be getting trapped. Get a plumbing to rework the pipe. To know for sure where the airlock, open your hot tap, and feel the pipe work where possible, where it goes from hot to a bit warm, there's you airlock
LTGF, August 2008