Direct (HWC).The directly- heated hot water cylinder is quite a simple system to understand. Cold water is fed in at the bottom where there is usually a small draincock. The water is then heated either by a dedicated boiler or an electric immersion heater in the cylinder. Bromley Plumbers are qualified for this type of job.A connection at the bottom of the tank feeds the boiler where the water is heated. The hot water is then returned to the hot water cylinder through a connection situated at the top of the cylinder. The hot water supply exits the top of the cylinder through what is called a T-joint. From this T-joint an expansion pipe called a vent pipe also runs away to the cold water storage tank in the loft.Indirect (HWC).The indirectly heated hot water cylinder has a heat exchanger (or coil) fitted inside. The water heated by the boiler passes through this coil and the heat is transferred to the stored water sitting in the cylinder. The water that is in the coil itself is part of a self-contained system and is never mixed with the water in the cylinder that is supplied to the taps. This prevents not only limescale build up in the boiler system but it will also extend the life cycle of the system as it will allow anti-rusting additives to be introduced into the boiler water. A Bromley Plumber understands these systems.The cold water feed enters the cylinder at the bottom where there is also usually a small draincock fitted ( same as the direct system). The hot water supply to the domestic taps exits the cylinder at the top through a T-joint and just the same as the direct system an expansion pipe called the vent pipe also runs from the T-joint to the feed and expansion tank in the loft.