Untreated water in a wet central heating system will naturally corrode metal components. Most poorly maintained or untreated hot water central heating systems suffer from the accumulation of thick sludge deposits. These deposits are usually a mixture of black iron oxide corrosion products, water hardness scales, casting sand, welding debris, non-ferrous metal flakes, paint particles and other undesirable material. The sludge particles can range in size from very large to less than a micron. The smaller particles typically bond to the interior surfaces of components, often causing wear and premature failure of pumps and valves. The heavier types of debris can settle at points of low water flow causing blockages and upsetting the balance of the system, resulting in loss of boiler efficiency and system effectiveness.