The water held in a central heating system would normally corrode steel or iron radiators. When a central heating system is installed a dose of system protector, or ‘inhibitor’, is added to the water. This prevents corrosion in the form of ferrous oxide (rust).
Over time the amount of inhibitor in a central heating system can be reduced. This happens as a result of topping up the water in the system. System leaks, draining radiators or adding new radiators would all mean adding water to a central heating system.
Once the dose of inhibitor has been reduced the process of corrosion starts and ferrous oxide is created. This solid is kept suspended in the water as it flows at high velocity through the system, but it will settle as a dark sludge where the velocity of water flow is lower.
Water flow velocity is lowest at the centre of a radiator. As the sludge settles in the same part of the radiator it gradually builds up and forms a solid mass. This build-up prevents hot water from coming into contact with that part of the radiator panel. This reduces the energy output of the radiator.
Radiators need to remain on for longer to reach the comfort temperature set for the room. This means the boiler is burning more gas as it’s working for longer than it would otherwise need to. Power flushing can help correct this.
A power flush removes sludge and restores performance of the central heating system.