there is a small tank in the rear of the boiler which is used to keep a reserve of hot water. this is used when you demand hot water to get it to the tap quickly whilst the boiler is heating the cold feed. after you have used hot water or the temperatute of the water in the small tank drops and the boiler will heat it up again. when the tank is up to temperature, a small amount of water is diverted to the radiatiors to dissipate surplus heat. Irritating but a functional part of the system
rob
September 2007