hi, i thought i'd just post this as i had been having a problem with my central heating saturday just gone. after reading various forums and trying the advice given about bleeding the rads, shutting the upstairs rads, sludge in the system etc, it turned out to be my pump. it was a grundfos selectric ups 15/50 and i bought a new one from B&Q. it was £74 but after discount, because my wife works there, we got it for £59. i fitted it yesterday and PRAISE BE! 
everything is back to normal again. hope this helps anybody with a similar problem.
everything is back to normal again. hope this helps anybody with a similar problem.
