Why power flush?

The water in a central heating system is constantly pumped in the same direction around a central heating system, steel radiators and other metallic components attached to the system will begin to rust internally, producing black iron oxide (Magnetite), commonly known as sludge. It can take a long time for this process to occur, though hard water is known to significantly increase rates of corrosion. This sludge along with other possible oxidisation deposits will move around the system and over time there may be a build up these harmful contaminants within the system, iron filings, corrosion and possibly grease and oil will slowly settle throughout the system, the pipes, radiators, valves and even the pump may all be affected by such deposits. Anyone who has removed an ageing radiator will have seen evidence of such sludge and dirty water. This build up not only restricts the flow of water throughout the system, making it work harder and possibly reducing the system life expectancy, it acts as an insulator, reducing the ability of a system to effectively transfer the heat within the water to the interior of the property. If you're noticing that your radiators are not getting as hot as normal, or as hot as you would expect them to (especially at their tops) and bleeding them has failed to resolve the situation, it's quite likely your heating system will benefit from a system power flush.

Symptoms to look out for

There are many and differing symptoms that indicate a power flush to the system may be required.

The power flush procedure

During a professional power flush, a flushing pump is temporarily connected to the heating system, water is mixed with special powerful cleansing chemical agents and then forced at high velocity (but low pressure to protect the system from damage), through the system in both directions. The speed of the water flow, coupled with the action of the strong cleansers (which help breakdown any crust formation on the sludge) and the agitation, caused by the bi-directional flow, help to dislodge and mobilise any sludge and/or debris. Radiators will usually be individually flushed without the need to disconnect them from the main system and high frequency vibration may be applied to loosen the more stubborn deposits, the unwanted sludge and debris is then expelled from the system by the machine and a final flush with clean water and a neutralising agent is made.

The system is then recharged with fresh clean water, along with special inhibitors to slow the build up of iron oxides, lime scale and other materials within the system and re-instatement of the system to normal operating procedure usually takes only moments. The whole power flushing process can take between 4 and 8 hours, dependent upon the the system size and its initial condition.

Performing a power flush is usually a highly effective method of cleansing a system of the aforementioned sludge, corrosion and debris, however the overall effectiveness will depend upon the period of time a system may have been neglected or run without previous treatment with a suitable corrosion inhibitor.

The results of power flushing

Power flushing helps to improve the effectiveness of a system to successfully transfer heat throughout it, in most cases the system will run as smooth and quietly as when it was first installed, it will also improve boiler life span by lessening the likelihood of blockages and allowing parts to move more freely. It is recommended that a boiler in excess of 15 years old is replaced to achieve highest efficiency and all boiler manufacturers insist that a power flush is performed on all central heating systems prior to the installation of a new boiler. Rules on power flushing are however covered by The Building Regulations Part L — Conservation of Fuel and Power regulation, which was developed in response to the European Energy Performance in Buildings Directive.

Possible problems

A consequence of power flushing is that problematic issues can be exposed by the procedure, such as leaks on pipes, joints or radiators, these leaks may have been on the system for some time but may have been clogged by the very substances removed by the flushing process. Such incidences are not too common or serious, but must be taken into consideration prior to undertaking a system flush, as such incidences may lead to additional costs being incurred.

Magnetic filters

Carrying out power flushes, adding an inhibitor (which needs to be monitored during the annual service), are known to be effective ways of minimising potential heating system sludge problems, but magnetic filters are another way to increase the life and efficiency of your central heating system. They are simple units that trap any sludge and debris before it can do any damage to your boiler and it's controls. Easy to install they will help keep your heating system running at maximum efficiency and maintenance is simple — it just needs to be cleaned during the annual boiler service.

There is an argument that magnetic filters are an unnecessary expense with good system maintenance, but newer models of boiler may have very narrow tube heat exchangers, or even a system of tightly spaced plates. These newer components have been designed to speed up the transfer of heat, but mean the heat exchanger may be more prone to blockages, so a modern magnetic filter, preferably one with gravity separation to capture non-metallic sludge such as oxidised aluminium, copper or zinc (which will not be caught by the magnet), may well be a wise precaution. More about magnetic filters [ here ].