The flood from the heat exchanger was novel. 5pm on friday I noticed a colour change on the hallway carpet, stepped on it and it squelched. Open cupboard door and floor is awash and multiple drips from casing front edge. I have no service contract on boiler so rang local recommended business but he is too busy and says call Vaillant or BG. I thought BG would have more resource to respond so rang BG. They explained the options available and I chose the fixed price repair/service and 12 month contract.( I knew the leak was mains related as the pressure had not reduced and it was leaking at least 1 litre/hour ,but not from the visible pipework) 12o'clock Saturday BG arrive and start looking for leak. He cann't find but there is lots of water sprayed over the lower half of the cabinet,so he isolates the mains supply and the leaking slows then stops. Lots of paper towel later he says he thinks the H/E is the problem, he was able to tighten the 4 corner screws that clamp the 2 halves of H/E together, restored mains and no leaks. Happy Days.