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Power Flushing

The diagram below shows a typical heating system and problem areas. With modern boilers particularly now with the advent of high efficiency boilers there is a need to ensure your system is clean before installation and treated with inhibiter when commissioning. There is an approved standard required by all manufacturers known as BENCHMARK to which installation must be carried out to ensure your manufacturers guarantee is valid.

Typical system design showing potential areas for problems 7 areas are identified by points labelled 1 -7 and are detailed in the text. All new systems should be pre-commission cleansed in accordance with BS:7593 and Benchmark. This ensures flux residues, excess jointing compounds, mineral oil and other contaminants that can be found in the system following installation, and that can effect the performance of the system or cause component failure, are removed. It is important when installing new boilers into old systems that all sludge is first removed from the system or this could accumulate in the new boiler and lead to premature failure. Additionally, in hard water areas existing systems will have accumulated limescale together with corrosion deposits in the heat exchanger, which could easily have reduced the boiler efficiency by over 5%.

Illustration of a pipe being flushed and an image of a poswer flush unit.

  1. Blockage in radiator valve Leading to incorrect operation of valve, no flow in radiator
  2. Pump seizure and failure The abrasive and magnetic properties of black oxide sludge increase shaft and bearing wear in pumps causing them to stick or fail.
  3. Cold spots The familiar cool low central area of a radiator indicates a build-up of black sludge sediment that restricts flow and reduces heat.
  4. When the top of a radiator is cold during operation, either air or hydrogen is to blame. Hydrogen gas builds up as a by-product of electrolytic corrosion and is flammable (due caution is required).
  5. Pinhole leak Water damage
  6. Black sludge in underfloor pipework Reduced flow or blockage in pipework
  7. Scale (limescale/iron oxides) in boiler Leading to reduced efficiency, increased emissions, higher fuel bills and boiler noise.

Power flushing is the most efficient and effective method of cleansing a central heating system. The principle is to create a powerful fresh water flow under controlled conditions to remove debris from the system. By connecting the power flushing unit to the heating circuit in place of the system pump, boiler or radiator the circuit can be thoroughly cleansed of limescale and corrosion debris. When used in conjunction with a Fernox cleanser a typical power flush can be completed in 3-4 hours.

with greatful thanks to FERNOX

The Benchmark Scheme

Since it was launched in 1999, Benchmark has provided a vital means for improving the quality of installation of heating and hot water systems by encouraging the correct installation and commissioning of appliances and equipment.

The Benchmark Commissioning Checklist
The existing Benchmark log book is currently in the process of being replaced by a new Benchmark commissioning checklist, an A4 double sided sheet that will be included in all HHIC gas boiler manufacturer members’ installation manuals. The checklist will help installers record more information about the installation, in order to assist with servicing and repairs, such as details of system cleaners and inhibitors, CO2 readings, and Gas Work Notification numbers. The checklist is referred to in the draft Building Regulations as an example of an effective checklist, demonstrating Benchmark’s importance as the standard Code of Practice for the installation, commissioning and servicing of central heating systems.