What Is A Power Flush?

09 May. 2019

Written by Neil Marsh MCIPHE RP RHP EngTech

What is power flushing?

Power flushing is the process where a high velocity, low pressure pump is used to loosen sediment and other unwanted matter (flux, solder, bacteria, etc) in a wet central heating system which then can be extracted from the system and so reduce the volume of contaminates/matter that could have a negative effect on the operation and efficiency of a system…

The correct way to do this is by adapting onto, or removing the pump from the system and connecting the power flush machine to the “heart” of the system. This can also be done if there are correctly located and dedicated connection points, in place for the purpose of power flushing. Power flushing central heating systems through radiators and other methods will often result in poor results and is not a recommended or approved process. However, power flushing a singular problematic radiator is acceptable.

To increase the speed of this process when sludge (ferrous oxide) is causing an issue, magnetic filtration may be used to improve the process, which will reduce the volume of water used.

What are the limitations?

Using correct methods, equipment and suitable chemicals at the correct doses will increase the chances of power flushing success. Strong acid-based chemicals (these require neutralizing with a separate product before being drained) will often be more effective than using a singular flush product that is marked as “environmentally friendly”. FORTHRIGHT stands by the use of dedicated, specialist power flushing acid chemicals such as Scale Breaker & FX2 instead of the use of such products as X800 on existing central heating systems.

Ferrous oxide, flux residue and limescale are the common solids that are found in central heating systems, these can cause blockages and restrictions in the heating system, reducing or even preventing the flow of water and the transfer of heat within the system. The power flushing chemicals advised and used by FORTHRIGHT, will often breakdown such unwanted matter and allow it to be mobilised in the system water by the power flushing unit. More serious problems, such as dense blockages and micro-bore pipework (8 & 10mm) can reduce the effectiveness of the process.

Micro-bore systems can be effectively power flushed. FORTHRIGHT has successfully treated many systems in Cheltenham, Gloucester and the surrounding areas of Gloucestershire, however as the smaller diameter pipes restrict the flow of water, power flushing is not always fully successful. Additional methods can be employed to successfully reduce the amount of sediment and other matter from radiators such as individual radiator flushing and draining the radiator individually post-treatment, however it must be understood that there are limitations to power flushing and the more obstacles put in the way of the process, the less effective it will be.

Aggregates that may have contaminated the system during the installation process (such as materials used as the house building process) will often not be broken down by the chemicals. The certain foreign matter that may have collected in the system may not be removed by the power flushing process. 

Although not common, FORTHRIGHT has witnessed this occurring in recently built properties where the heating systems are installed in stages and the workmen have left heating pipes open during the first fix process allowing debris from the site to contaminate the heating system. In instances where FORTHRIGHT have suspected this, especially where singular, lower floor radiators have been the issue and we have advised that further investigation is undertaken to remove possible physical blockages before advising a power flush.

FORTHRIGHT adheres to the Approve Codes of Practice such as those set out by the Domestic Water Treatment Association and ensures treated water is physically examined, checked with a TDS meter (the total dissolved solids) to within 10% of the tap water supply and PH checked prior to inhibitor treatment.

Small pockets of discoloured water and/or sediment can be caught in radiators where the flow is restricted by such things as radiator size, location, pipework diameter and length of pipe run will affect the flow. When this happens it is generally in one or more of lower level radiators, often it will just be a small amount of fluid in the bottom of the radiators that will run clear after a short while of drawing water off the radiator. Hence FORTHRIGHT advises that full-bore drain off valves on the tails of radiator valves are fitted on all low lever radiators to ensure any such solution/sediment can be drained off successfully.

Header tanks that feed conventional central heating systems are disconnected during the process to prevent fluid overflow back into the tank. Over long periods, header tanks can become heavily soiled with contaminants such as sediment and when reconnected to the system will reintroduce unwanted matter back into the heating system. Where a header tank is accessible and contaminated, FORTHRIGHT advises that the tank is removed and cleaned out, however, inspection and/or removal are not always practical, due to possible locations. In such instances, if the client is not willing to pay for a replacement tank, the client must accept that sediment and other contaminants will possibly re-enter the system.

Due to the nature of power flushing, defects such as weak points in the system can become evident. It could be that a faulty radiator valve begins to leak during the process because sediment has been removed. Problems with radiators & pipework may become visible because the cleaning process has removed the corrosion/scale/sludge thus highlighting the weak points. Although not common, if these problems do occur the cost of power flushing does not include the cost to such defects.

Is it effective?

Overall, power flushing is a very effective way to make significant improvements to the longevity and efficiency of a central heating system. A contaminated system will often have increased maintenance costs, plus and decreased efficiency, which over time will lead to increased operational costs.

In FORTHRIGHT’s experience, the majority have contaminants present that are having a negative effect on the system. The severity of this effect is often dictated to by the level of contamination. Repairs to the boiler and central heating systems will be reduced by ensuring that the water in the system is of a good quality.

We have yet to find a system that has been contaminated that has not benefited from a correctly applied power flush, with the exception of complete solid blockages to main flow and return pipes.

Common problems caused by contamination of a central heating system.

Conventional systems:

Radiators heating up when systems demand is for hot water only.

Hot tap water getting scalding hot.

Hot tap water failing to heat up.

Reduced pump life.

Reduced motorised valve life.

Kettling (rattles & bangs) from the boiler.

Overheating of the system.

Cold spots in radiators.

System water pumping into the header tank.

Thermostatic radiator valves failing to work.

Combination (Combi) boilers:

Radiators heating up when systems demand is for hot water only.

Hot tap water getting scalding hot.

Hot tap water has fluctuating temperatures.

Hot tap water failing to heat up.

Reduced pump life.

Kettling (rattles & bangs) from the boiler.

Overheating of the system.

Cold spots in radiators.

Thermostatic radiator valves failing to work.

An example of what can be in your heating system.

A recent job that FORTHRIGHT undertook in Gloucester to power flush a system was showing a mild black/brown tint to the water prior to the power flush being undertaken. Once the chemicals were added to the system and all radiators where flushed, this is the colour the water in the system became:

The customer has a contract with a large energy supplier to ensure their heating system, however the terms of their contract, like most if not all the insurance/maintenance contract suppliers, specify that the removal of sludge, scale and any other sediment, including any damage to the system caused by such things being present are not covered under policy. In this instance, the pump struggled to operate due to the heavy formation of sludge on the impeller, which therefore damaged the pump. Although the system was successfully cleaned, unfortunately, the damage to the pump too severe and FORTHRIGHT advised that they replace their pump, which was not likely not to be covered by their insurance policy.

A pump in an average house can cost up to £250 to replace, motorised valves such as 2-ports and 3-ports valves are expected to cost up to £200 to replace, however, we have seen materials that cost far more than this.

System water analysis

Generally, heating engineers will diagnose sludge and scale in your system through experience and visual detection. Sediments such as ferrous oxide, when in sufficient quantities will be visual in the system in the form of sludge or discoloration of the water. Scale, however, cannot be detected visually in the water and only becomes noticeable when it solidifies to form a white deposit. Scale deposits around weeping joints, in pipes, fittings and components are often how scale can be diagnosed as well as other system complaints.

Using a visual analysis (Turbidity Tubes etc), experience and TDS meter is good practice for identifying the presence of sediment in a system. However, this method will not tell you exactly what is in the system, although the likelihood is that one or more of ferrous oxide, scale or flux residue will be the culprit(s) for any possible future problems. This method, along with experience will gives us a good idea of what the problem will be.

A basic test kit can be used to help identify approximate levels of the contaminants in your system, however, the only true way to identify exactly what is present is to collect several water samples and have them tested in a laboratory. Generally speaking, this is an expensive process and would not usually be undertaken.

Post flushing

After the system has been fully flushed, inhibitors are used to reduce the corrosion process, the accumulation of limescale and biological contamination. The full effectiveness of inhibitors is debatable, as most of the product research usually comes from the manufacturers. There are several brands that vary in their effectiveness, no one can really tell you which of the products are the most effective, however in our experience most appear to work efficiently when added to a correctly cleansed/power flushed system. We have witnessed systems as old as 10 years with little or detectable scale or sediment formation, providing that the correct flushing and inhibitor process was applied.

Usually, 1-2 tubs will be enough to treat an average heating system, most brands will work on 1 tub per 100 litres (or 10 radiators as rule of thumb).

One thing to note with inhibitors (brand dependent) is they can discolour the water slightly following treatment, depending on colour of the product, this can make it look like the water has become contaminated, which is not the case. We have yet to find an inhibitor product that has not increased TDS meter readings following treatment. Inexperienced engineers can be fooled into believing that a heating system is in need of power flush when actually it is just the inhibitor in the system water causing discolouration or higher TDS meter reading.

The three brands FORTHRIGHT have confidence in are Fernox F1, Sentinel X100 and Corgi Inhibitor.

Click here to read why magnetic filtration is not a substitute for power flushing and a more information about what failing to flush a central heating system correctly can do.

If you are in need of a power flush in Cheltenham, Gloucester, Tewkesbury, Stroud or any of the surrounding areas, then call the professionals and call FORTHRIGHT.