I did get it from the shop, only reason I asked was because I know sometimes RMAing something usually involves having to wait days for it to be tested etc. but the fact is I can't really afford to be posting it back and forth and my only means of getting to the shop is a long bus ride and a fairly long walk.
I followed your advice stulid and the tapping didn't help. The tubes are actually quite firm but I didn't feel anything and despite the super high temperatures (90+) the tubing and radiator are really cold to the touch. I'm guessing the pump simply isn't pushing the water around, not fully sure what the noise it makes when I turn the system on is though as it does kind of sound like it's starting up. Maybe it just doesn't get going.