Urgent help needed

[mylesy]

does the cylinder have an anti vacumme valve fitted?

 

[mylesy]

theres two types of vacumme that you can get. if the cylinder is high up, when a tap is opened at low level it can pull on the cylinder. the other thing is is when there are long runs of hot feeds, when there has been an open tap and hot water is flowing, when the tap is turned off the expanded hot water cools and pulls on all the pipe work, finds week points and draw air in from taps and such. again without being there hard to say. anti vac valves are easy to fit by the way, you'll have no probs getting one too mate.