The block of flats I live in has a large cold water attic tank with an overflow pipe that is permanently running. A plumber drained the tank and capped its supply, assuming no one in the block was still using it. Within two days (no idea how long though) the tank had filled back up and the pipe was running again. The cap is definitely working.
How could this be happening? I can see from outside that everyone in the block has flues for a combi (?) boiler, so could it be a faulty mixer tap or mixer shower in someone's bathroom is allowing mains pressure (hot, from the boiler) to backfill a pipe that is still connected to the attic tank?
How could this be happening? I can see from outside that everyone in the block has flues for a combi (?) boiler, so could it be a faulty mixer tap or mixer shower in someone's bathroom is allowing mains pressure (hot, from the boiler) to backfill a pipe that is still connected to the attic tank?