Kassee - sorry, our latest posts have overlapped and I have just noticed your latest reply. I thought you already had new boiler installed. I would get leak looked at ASAP as it will still be leaking even though heating is off. I would just get a plumber to look at it, by personal recomendation if possible - should be no more than min callout charge to fix, unless tank is damaged, but they are not expensive. Whether your current service engineer is a plumber as well, you will need to ask. If he/she is independant, they probably are - if British Gas, probably not.