Power flushing is a process where an entire heating system (pipework, radiators, etc.) and possibly the boiler itself are forcibly cleansed by a generating high-velocity flow of water through the system. The motive power is provided by employing a high-capacity pump delivering flow rates of up to 150 litres/minute (10 times more than an average sink tap).
Almost invariably some form of chemical cleansing agent is employed to assist the flushing process and it is generally desirable to introduce heat into the system to speed any chemical reaction that is taking place. Chemicals used range from moderately strong acids to attack and break down impacted and hardened sludge deposits to non-corrosive cleaners which raise soft sludge into suspension and bind it together to form larger particles that are easier to flush. Choice of chemical depends upon the type and level of system contamination and the condition of the system, a very old system may not survive flushing with an acidic cleaner.
A recent addition to the cleaning process is the employment of a high-power magnet to attract and retain suspended ferrous particles. This prevents the contaminants being recirculated and thus speeds up the cleaning process.
Numerous reason but it can be generalised that hydronic heating systems (those that use water as the heat transfer medium) incorporating components containing iron (steel radiators, etc.) are susceptible to contamination with ferrous-ferric oxide sludge. Ferrous-ferric oxide (Fe3O4), commonly known as magnetite, is a commonly occurring type of iron oxide, it is black in colour and naturally magnetic.
In a system that is experiencing operational problems resulting in the continual addition of fresh oxygenated water, significant oxidation of the iron can occur generating an incredible amount of sludge. The magnetite concentration can build up to the point where the system water becomes black and almost viscous. The sludge whilst still mobile settles in areas of low flow velocity, such as radiators where it will cause circulation problems and limits the system’s ability to gain and emit heat, basically preventing it from achieving its primary function.
Cold bottoms on radiators, noisy boilers, poor circulation due to pumps clogging are all symptoms of sludge contamination but the real issue is one of efficiency and ultimately component failure. Contaminated systems cost significantly more to run than those that are clean, according to the Energy Saving Trust contamination can cause up to a 15 per cent reduction in system efficiency. The other major issue being premature component failure, this can be pumps, valves etc. or even the boiler itself.
If your system has any of the following signs or symptoms then an assessment should be carried out to see if flushing is necessary.
If a system requires a power flush it is generally in poor condition and will probably contain a large amount of ferrous –ferric oxide (magnetite) sludge. This sludge has been generated by the corrosion of iron containing parts of the system and it is not uncommon for very old radiators to develop pin-hole perforations. The process of removing sludge from a system may indeed expose pre-existing defects resulting in minor leaks. However, if the system was in such an advanced state of decrepitude then failure would surely occur within a short time period regardless.
The other concern is pressure but in reality the consequential pressure increase within the system that occurs during flushing is never excessive and only minimal risk of damage to the system is presented by it.
Modern high-efficiency boilers are far more complex than traditional designs. Waterway in traditional boiler heat exchangers was up to 10mm in diameter, in a modern condensing boiler this can be as small as 1mm. The consequence of this is that modern boilers are very sensitive to sludge and particles of rust, scale, etc. that is present in the existing heating system onto which a new boiler is fitted. If a failure occurs where sludge or debris is found present in the new boiler, it could void the manufacturer’s warranty.
We use the Kamco CF90 Quantum2 Powerflush pump combined with a Kamco CombiMag magnetic filter. This high-power pump delivers flow rates up to 150 litres/minute, more than double most other pumps on the market. The CombiMag uses a high-power rare earth magnet to capture magnetic sludge particles preventing them being recirculated and thus reducing flushing time.