Purchase your copy of BS as a PDF download or hard copy directly from the official BSI Shop. All BSI British Standards available. Power Flushing for central heating systems Compliance with Building Regulations Part L (BS ). Products. CalFlush Power Flushing Unit. by a new boiler. Many boiler manufacturers now make the warranty dependent on flushing and cleaning in accordance with BS, Benchmark and Part L.

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It is one of the aspects of “Water treatment” required at certain times to maintain the correct working of a heating system. There is a British Standard document BS Flushing is a process of running or pumping water possibly with the addition of chemical cleaning agents through the pipework and radiators of a heating system, so as to help dislodge and remove accumulated deposits of sludge and other undesirable contaminants that will be detrimental to the life or performance of the heating system.

The flushing water is ultimately sent to a foul drain – along with any contaminants carried in it. The term “sludge” is often used as a “catch all” to describe all the different contaminants in a central heating system.

Different types can be caused in different ways, and in some cases, require different treatment to remove. Sludge is usually a mixture of corrosion by products such as rust or magnetite magnetite is a black magnetic corrosion by product one one gets from steel when it corrodes in a low oxygen environmenthard water scale, and particulate impurities introduced into the system make up water.

When water is heated, insoluble calcium carbonate is formed which can then come out of suspension to form deposits on surfaces within the system this often referred to as “lime scale”. While it is most likely to form in the boiler’s heat exchanger, it can also accumulate elsewhere in the system, often at places where the water circulates more slowly.

Under normal operating conditions non-bicarbonate or “permanent” hardness salts, e. The potential for scale formation is greatest in those hard water areas of the United Kingdom where the bicarbonate alkalinity is high.

Power Flushing – Calmag Limited

Scale formation will be most pronounced if there is a high rate of water loss from the system, requiring frequent addition of fresh water to the system. Scale in the heat exchanger will have a detrimental effect on boiler heat transfer efficiency. Scale can also be responsible for boiler noise or “kettleing”. Microbiological organisms range from simple bacteria to fungal and yeast spores.

All of these can flushibg problems when they enter a central heating system. The most likely place for microbiological growth exists in the feed and expansion cistern of an open-vented system. Here the temperature conditions are more favourable for bacterial growth and there is contact with the air. Aerobic bacteria, fungi and slimes which have developed in the cistern can enter the system with the make-up water and produce debris.

Such debris can cause blockages and is liable to foul the boiler heat exchanger. Anaerobic bacteria can thrive in both open and sealed systems fouled with corrosion and other debris, beneath deposits where fluushing temperature might be lower and there is an absence of oxygen. This can give rise to microbiological corrosion of iron or steel compoents. System areas most prone to failure due to fouling by scale or sludge include the boiler heat exchanger and circulator pump.


Fouling can also restrict flow through components such as thermostatic radiator valves, zone valves, drain valves, etc.

A system will need an initial flushing after installation to remove any residue of flux or pipe jointing compounds, plus any metallic particles such as swarf left over from recent pipework installation or changes.

If the system is correctly maintained, well designed, and regularly treated with a corrosion inhibitor, then it is unlikely to need deliberate flushing until significant changes are next made to the system. However its common for not all of these ideals to be met, and excessive sludge can be the result. Clues that sludge may be a problem include:. Systems should also be flushed thoroughly prior to the installation of a new high efficiency condensing boiler, since the heat exchangers in these are particularly susceptible to damage from contaminants in the heating system.

Before cleansing, the system should be examined to determine the system configuration and the age and overall condition of components, in order to ascertain the cleansing regime required. For example, the procedure could remove corrosion debris covering pin-holes in radiators and this could result in leaks. If there is any doubt as to whether a system will withstand any cleansing methodology, then replacement or repair of relevant components will be necessary before continuing.

There are a number of ways that a system can be flushed, and there are a number of treatment products on the market designed to aid in cleaning and flushing heating systems.

Many products are designed to be added to the circulating water some time prior to flushing, and aid the mobilisation of contaminants prior to flushing.

Follow the manufacturers instructions. Powerflushing is arguably the most effective procedure although it is important to check the boiler manufacturer’s instructions to establish whether powerflushing is acceptable with the boiler in circuit. Powerflushing is a particularly effective method of cleansing existing systems, especially those containing a high level of black magnetite sludge. Note with all techniques, reversing the flow will help to remove debris which might otherwise remain trapped.

Prior to flushing by any method there are some common preparation steps. These will typically include adding an appropriate cleaning chemical to the working system and running it normally for a time prior to the actual flushing. The cleaner is usually dumped while hot from the system, and the system refilled to start the flushing process.

While there are many companies that specialise in offering this service, it is also possible to hire the equipment and do it yourself.

Customers being ripped off – Power flushing.

Since the exact procedure will depend on the equipment this section only outlines the basic procedure, please follow the detailed instructions supplied for your equipment. Follow the manufacturers instructions for connection of the machine.

Note that powerflushing is normally more effective at higher temperatures.

Some systems allow the boiler to be operated at the same time, others may include some heating capacity of their own. Mains pressure flushing may require temporary alterations to the system to make appropriate connections to the system.

Not all systems will have a connection flushimg a supply of mains water however, and even those that do i. Hence it is often worthwhile making up some adaptors to enable a hose to be connected to the tails of a radiator. Thus by removing a radiator and then connecting to either the flow or the return tail and capping or shutting off the other tail! Note to comply with water regulations, it is important that any hose used includes or is fed from a tap which bs75593 a non return valve aka a “doublecheck” valveto prevent any possibility of bs75593 of the mains supply.


Unless one is specifically attempting to clear a boiler blockage problem, it bs593 usually better to isolate the boiler via its service taps prior to flushing, to save the risk of pushing more sludge etc into the boiler itself.

If it is possible with your flushing arrangement, repeat the flushing process with the flow in the opposite direction. Gravity flushing is the least effective cleaning system, and may not work at all for clearing some blockage problems – especially if the system has been designed such that it includes pipe loops that do not readily fill and drain under gravity alone.

The vibration combined with the flow of the flushing water glushing free more sludge that may have settled and congealed in the radiator. You can also buy rubber faced accessories that fit into a SDS drill.

Used in “roto stop” mode, these allow the radiator to be vibrated mechanically using the drill during the flushing process. Rather than flushing all radiators in place, its also possible to use the “hosepipe method” ns7593 flush an individual rads that are giving indications of being badly sludged.

To do this, first isolate the rad with the valves either side, and then drain into a suitable tray by partially undoing one of the rad valve unions to bs75593 radiator. Once the rad is empty, undo both connections and place plastic bags over each tail, secured with rubber bands this is to catch any extra sludge falling out when the rad is moved, which is particularly bs75933 in carpeted areas, since the black iron laden sludge will cause significant staining if spilt.

Now the rad can be unhooked from its mounting brackets carried outside flushimg a suitable drain etc, turned on end, and flushed with through with a garden hose and repeated from the other end. This will often shift more sludge than is possible flushing in situ. Individual radiator flushing can make the flushing process more effective overall, especially when limited to a less effective system flushing process like gravity flushing.

Central heating flushing

Inhibition devices should be installed in the system pipework after bw7593 final flush and before the final fill with fresh water. Chemical inhibitors should be added at the time of final fill with fresh water. Refer to the manufacturer’s instructions. Under no circumstances should the system be left empty for extended periods as this could accelerate corrosion of ferrous components like radiators. A good quality corrosion inhibitor suitable for the system should be used.

The system water should be checked at intervals specified by the product manufacturer to ensure adequate ongoing protection. Unless the manufacturer’s instructions state otherwise, products from different manufacturers or different products from the same manufacturer should not be mixed.

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