Water has begun to pour out of my overflow pipe (not the toilet overflow). It only started within the last week and is intermittent. Running off hot & cold water doesn't seem to help, neither does turning off the boiler (which is usually on 24/7). The pipe doesn't appear to be from the cold water storage tank, which is in the loft, as it exits the external wall between the ground floor & first floor, about a foot below the outlet pipes from the bathroom. Can anyone tell me what this is for, what the problem is likely to be & whether I need to call a plumber. Help is needed urgently if I want to avoid getting a shower when I step out the back door!