It's a Grundfos central heating pump 15/60. It looks relatively new, although it is at least 8 years old, in that it's clean with no leaks or corrosion. The issue is that its not pumping. I've removed the bleed screw and I'm able to freely rotate it, so it's not jammed and I've used a voltmeter and the electrics seem fine. From reading around it seems that it needs replacing, but before I do is there anything else that I can try? Many thanks