Focus on powerflushing

Powerflushing 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 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.

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

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

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.

✘Don’t attempt to powerflush old systems with galvanised steel, 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.

BS 7593: Code of practice for the preparation, commissioning and maintenance of domestic central heating and cooling water systems

Keeping central heating systems clear of sludge, scale and debris is key to maintaining heating system health and efficiency. Here, Richard Crisp, head of chemistry at Fernox, looks at powerflushing, why it is necessary, and how to keep systems clean.

When water comes into contact with the metals in a central heating system, corrosion can occur. If left untreated, limescale, sludge and other corrosion debris will build up. Once formed, this debris can circulate and lodge in pipework and vulnerable system components, causing blockages that force the system to work harder, resulting in higher fuel bills. Over time, it can even cause system breakdown.

The good news is there are ways of cleaning the system to remove sludge and debris, and restore system health and efficiency. BS 7593:2019 suggests cleaning the system using a recognised method like powerflushing in the following situations: • If the system is heavily contaminated – signs of this include a sluggish, noisy system that takes a long time to heat up, and cold spots in the radiators. • When a new radiator is installed or extra pipework is added – to re-commission the system and remove any installation debris, oil and grease. • When a new boiler is installed – the system should be cleaned either before the boiler is fitted or when it is isolated from the rest of the system, to prevent existing contaminants from reaching or depositing in the boiler and causing lasting damage.

The Benchmark Commissioning Checklist, which acts as documented evidence of correct boiler installation and servicing, supports this by requiring confirmation that the system has been flushed and cleaned, and identifying the brand and type of cleaner that has been used.

A powerflushing unit sends water at high velocity through the system to dislodge and remove debris, limescale, and sludge build-up. A thorough powerflush will improve heat distribution throughout the property.

To accelerate and aid the cleaning process, pH-neutral, citric acid-based cleaners can be used. They are designed to remove contaminants in heavily sludged central heating systems, to restore and maintain optimum efficiency and reduce the risk of breakdown. Always check that the formulation is non-foaming because this will reduce the time needed on site to remove residual cleaner from the system.

After cleaning the system, BS 7593:2019 suggests dosing with a high-quality inhibitor to maintain cleanliness and protect the system. Inhibitors work by creating a barrier between the metal surface and the circulating water, preventing corrosion and the formation of sludge and scale.

It is important to make sure that the system is dosed correctly, to ensure full protection. To eliminate the chance of accidental under-dosing, you can choose a

product that treats the majority of systems with one bottle. The inhibitor should also contain three different types of inhibitor molecule: • Organic inhibitors, which bind to the metal within the heating system to protect from debris • Anodic inhibitors, which react with the system’s metal surface to create a protective layer • Cathodic inhibitors, which combine with hard water salts to form an insoluble layer.

Always check that the inhibitor is suitable for all types of boiler, radiators and pipework systems as well as all metals and materials commonly used. For added

protection, the inhibitor should incorporate a pH buffer because this keeps the system at a constant level and prevents pH levels from dropping below 6.5 or above 8.5 – the optimum pH range for preventing corrosion.

BS 7593:2019 suggests checking the inhibitor concentration levels on site as part of an annual maintenance service. This can be done easily and quickly with testing kits that indicate the level of inhibitor present within seconds.

It is also important to remember that inhibitors work hand in hand with in-line system filters to prevent scale, sludge and debris from causing lasting damage.

An in-line filter should be installed permanently to provide continued protection and maintain system efficiency. It should also be serviced as part of the annual boiler maintenance and according to the manufacturer’s instructions, to remove any sludge or debris that has been captured. This will ensure that the filter continues to work at its best, removing contaminants from the system.

Powerflushing, together with effective chemical water treatment and filters, is an easy way to keep central heating systems working at optimum efficiency. ■

BS 7593:2019 – Code of practice for the preparation, commissioning and maintenance of domestic central heating and cooling water systems

There’s no one-size-fits-all approach to successful flushing: each heating system needs to be treated individually, says Powderflush’s Stephen Kukard.

Ihave been cleaning central heating systems for more than 10 years and can’t help but notice how different jobs have become over time.

Straightforward open-vented systems, with all-copper pipes and single zones for heating and hot water, have become a rarity. It is much more common to find a sealed system with microbore plastic pipes for the main heating system, rubber hoses in the boiler and underfloor heating covering two or more rooms with its own pump. For this system, at least three connection points are needed to clean it correctly.

With modern systems being different and more complex, heating engineers need to up their game and learn new techniques to clean them. No two heating

systems will respond in exactly the same way to being cleaned, and each system has to be treated in its own way.

Some systems will actually block up more when you try to clean them: my advice is to start flushing up the return pipe, and always flush the closest radiator to your machine first. By flushing the system in reverse, the blockages are pushed out towards your machine and filters rather than compressing them.

Always double-check what your client is telling you: they are not professionals and they get it wrong all the time. Unlike the professionals, they often only touch the top of their radiators, and often compare the halfworking ones to the ones that don’t work at all. That can lead to confusing accounts about their issues and set you up for a rough start.

Many of my clients would think that two of their radiators are not working correctly but,

after an initial walkthrough, I would discover that five of them are already in various stages of blocking up and two are completely blocked. It’s all about sizing up the job correctly: the fewer radiators that are blocked or partially blocked, the easier it should be to clean that system. As a rule of thumb, if 40 per cent or more are blocked, it’s unlikely that a powerflush will resolve all the issues.

A common error is to assume that systems containing black water have more sludge in them than ones where the water flows seemingly clear. Clear water in a sample does not always mean a clear system. Newer systems have different types of pipe and metal in them, each one causing sludge to form and block up differently.

Some materials condense the sludge into small, hardened flakes lies in the system, leaving water seemingly clear, while others build up on the pipe walls. You can often recognise systems with sludge flakes because the water sample has an unusual smell and there are small pieces of sludge flakes while being a seemingly clear sample overall.

To increase your chances of cleaning a modern central heating system successfully, connect on the largest pipes possible to get the best flow rates. You might

need to connect your machine in multiple locations to be closer to the blockage to force it to break apart. It’s also a good idea to use heat and chemical cleaners wherever possible to soften up the more stubborn pieces, while focusing down your flow to a single radiator at the time.

I would recommend using as much magnetic filtration as you can, as your filtering capacity does matter on bigger systems. The more magnetic filtering, the less cleaning, and the faster the job finishes.

The most sludge I have taken out of a system is 15kg from just 15 radiators – the customer had described their system as just heating a little too slowly.

Some customers wait much too long before they call in the experts and, in some cases, the systems have become too blocked for powerflushing to get it back to 100 per cent functionality – make sure you give your clients a realistic assessment about the chances of success.

And remember to always clean the whole system, not just part of it. Sludge moves around over time and tends to block up in the same places as before.

Leaving sludge in any section of the system will probably result in a callback for the same issue. n

Now you see sludge; now you don’t