DIY Doctor UK DIY Forums

I have a leaking hot water cyl to replace. The return pipe from the boiler has a gate valve but the feed has not will this be ok when the cyl is drained :?: Also i have an expansion tank in the loft as well as CW storage do i need to do anything with the exp.tank to replace HW cyl :?: Finally ,exp.tank has been filling and coming out of overflow now and again could this be due to leaking HWcyl or not as ballcock valve seems ok :?: THANKS