REGISTERED GAS ENGINEER | POWERFLUSHING
Study and survey first You should only powerflush a heating system after you’ve made a thorough study of it, writes Kamco’s Keith MacBain.
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owerflushing domestic heating systems has been established for decades. The principle is sound, and is based on methods used on commercial systems for many years. It is water velocity that moves debris, not pressure, and this is why BS 7593 suggests that heavily sludged heating systems will benefit most from a powerflush. The same standard advises that a cleaning chemical must be used during a system clean, and it is simple to add to the powerflushing pump tank when starting the flush. While some heating engineers will opt for a mains water flush only, the flushing chemical must then be added on a prior visit and not on the day of the system clean. A further downside is that, without a powerflushing pump, the requisite high water flow rate is not available when the mains water supply pressure is low or fluctuating. The high water velocity provided by a powerflushing pump will loosen and mobilise debris that the standard system circulator pump simply will not move. Used in conjunction with a good flushing chemical, cleaning can be taken to a much higher level. The need for system cleanliness is even more vital as boiler manufacturers compete to give longer warranty terms on their new boilers. It is good news for householders, but that guarantee
“It’s water velocity that moves debris, not pressure, which is why heavily sludged heating systems will benefit the most from a powerflush.”
has to be earned by the engineer, with a requirement for a high level of system cleanliness to protect heat exchangers and other components from the problems caused by corrosion debris. Boiler manufacturers are very aware that, in the early years of a new boiler, more than 80 per cent of service calls are related to poor water quality. Study and survey While powerflushing is regarded as the most effective method of system cleaning, the decision can only come after a thorough survey and examination of the system: What are the clues to look for? 1 The system is slow to warm up 2 Some radiators are completely or partially cold when the system is operational. Heating engineers often use an infra-red thermometer or camera to assess the degree of fouling 3 The radiators are not getting very hot even with the valves on maximum, but the pipework running to the radiators is hot 4 The radiators need frequent bleeding as a result of gas generation (hydrogen is a by-product of the corrosion process) 5 Water samples taken from radiators are dirty and discoloured
Before committing to a powerflush, don’t forget to study this list of dos and donts: it’s always a good idea to use a survey form to note the details. Always read the instructions for the powerflushing pump or study the brief guides attached to each pump before starting your first flush. Familiarise yourself with the manufacturer’s helpline number Check the type and number of radiator panels, and their condition Check the make and type of boiler. Does it have an aluminium heat exchanger and therefore requires extra care in the choice of cleaning chemical? Check the age of the boiler: is it new, and should you isolate it from the system before flushing? Consider whether you should even be powerflushing the heating system if it is poor condition Take and evaluate a sample of the system water Check for reasons why corrosion has been taking place, and plan to remedy these Consider where you can safely discharge the dirty water into a foul water drain Always flush every radiator individually Check the water quality, clarity and pH after the flush, and before adding corrosion inhibitor.
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on’t attempt to powerflush old systems with galvanised steel, D stainless steel or low-quality copper pipework – and ask for advice if you are unsure Don’t powerflush a heating system with a primatic cylinder (it’s time to upgrade these inefficient systems) Don’t quote for a powerflush without first firing the boiler and checking all the radiators for heat-up Don’t forget to cap off/isolate the feed and expansion tank very securely in vented systems Don’t push the discharge hose down a toilet without tying the hose to a seat hinge or trapping it securely with the toilet seat Don’t leave a powerflushing pump running while you attend to a job in another house. Don’t be be put off by all the these dos and don’ts: tens of thousands of powerflushing pumps are in use in the UK, and the procedure soon becomes second nature. a) There are black particles present in the water. These are most likely to be magnetite. This is the final stage of corrosion, and large deposits can be expected in the system b) If there is a reddish tinge to the water, it indicates that red iron oxide is present, suggesting active corrosion and the presence of a lot of air in the water. Check for air ingress or ‘pumping over’ 6 One or more radiators have failed and have pin-hole
perforations 7 The boiler is making kettling noises 8 The circulator pump is heavily fouled and needs replacing frequently. If these symptoms are present, powerflushing is recommended, and by now the engineer should have learned a lot about the heating system to help them in the clean. n www.kamco.co.uk BS 7593: Code of practice for the preparation, commissioning and maintenance of domestic central heating and cooling water systems
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