Cheers for all the replies, i will try this! The thing that scared me
was that whilst i knew the Central heating wasnt working and not to
turn that on, i didnt realise that we'd have no hot water!

I hope that pump didnt run dry too long! It was making a thumping
noise and got very warm! I thought that the hot water for your tank
was mains fed (off teh main cold water tank)... How would I have
introduced air into this (seperate?) system!

CheeseyToastie