Shut off any hot radiators, and turn the pump on and off several times. Ensure the speed is set to three. This may force the airlock into the rads. IF this doesn't work you need to open up a coupling and allow a larger quantity of water to escape bringing the air with it.
Water circulating through the header tank introduces oxygen into the closed system. This will eventually cause corrosion to the rads and the resulting sludge can block both rads and pipework.
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!