5 problems with closed circuit systems and how to solve them

The problems encountered in closed circuit systems are like those in open systems, such as scale and corrosion. However, the fixed volume of a closed system allows for water treatment products to be dosed at much higher levels than is possible in open systems, where water is constantly lost to drain.

In this blog post, we have compiled a list of the most common problems our customers encounter when involved in the on-going maintenance and testing of closed circuit systems. For each problem, we have identified the closed circuit chemicals that are most effective at solving for them.

Problem 1: Scale build-up

Scaling is not generally a problem in a closed circuit system, unless there is substantial hard water make-up. But in the event that excessive deposits of calcium carbonate have built-up within the system, an on-line descaler, such as Multitreat OL, can be added to gradually remove scale during the normal operation of the system.

Removing the calcium carbonate scale from the internal surfaces will prevent under deposit corrosion and also increase heat transfer efficiency, thus saving energy.

Product Activity Details

Multitreat OL

On-line descaler
  • Use in central heating systems.
  • Polymer/phosphonate based.
  • Can be left for long periods, in a system, until scale is removed.


Problem 2: Elevated copper levels

If there are elevated levels of copper in the closed system, an azole may be added to maintain a protective chemical layer on top of the copper surfaces. Inhibitors that contain enough azole (a yellow metal corrosion inhibitor) to protect small amounts of yellow metals within the system are most suitable.

In systems with any significant amount of copper pipework it will be necessary to add an additional yellow metal inhibitor to the system to ensure that all the yellow metals present are protected against corrosion. B&V Chemicals’ range includes several azole supplements. Contact our technical department for guidance on which azole supplement would be most suitable for your system.


Problem 3: Foaming/champagne effect

Foaming in closed systems is rarely a problem but does occasionally occur. In the majority of cases, foam within a closed circuit system will be caused by a combination of high flow rates and/or system design. The addition of very low doses of specialised antifoam can alleviate these problems.

Product Activity Details

BV5 AF 49

Closed Circuit Antifoam
  • Controls foaming in closed systems.
  • Mineral oil based.
  • Use sparingly.


Problem 4: Reduced nitrite levels in multi-metal inhibitors due to NRB activity

If a multi-metal inhibitor such as B&V’s Polyhib CH is being used in a closed system, and testing indicates that the correct levels of Molybdate are present (i.e. >330ppm at 1%), but nitrite levels are depleted (i.e. significantly less than 250ppm), it is very likely that Nitrite Reducing Bacteria (NRB) are, or have been, active within the system.

In this case, the addition of a suitable biocide is recommended. This should be allowed to recirculate for at least a week until testing shows that total viable count (TVC) levels are under control. Addition of a neutral nitrite supplement is then recommended to bring the nitrite levels up to >250ppm as sodium nitrite. The most appropriate product for this application is the Polyhib HN5.

Supplementary inhibitor Composition Details

Polyhib HN5

Nitrite based
  • High concentration neutral product.   
  • Can be added to multi-metal inhibitors to replenish nitrite levels which have been lowered by the activity of NRB’s.


Problem 5: Extensive biofilm within a system

In some systems, the addition of biocide consistently fails to bring microbial numbers under control. One of the main reasons for this is likely to be the build-up of biofilm within the system. The layers of biofilm protect the bacteria from the activity of biocides and as biofilm levels deplete over time, bacteria are released from the biofilm to proliferate in the system once again.

A very specific closed circuit biofilm remover can be used in order to lift the biofilm from the pipework surface. The additional benefit of using a bio-dispersant within a closed circuit with biofilm is the fact that removal of the biofilm from the pipework surfaces will prevent under deposit corrosion and allow the corrosion inhibitor full contact with the metal surfaces.

There are two products effective at removing biofilm in closed circuit systems. Both should be used in conjunction with a biocide, so that as the biofilm is removed microbial numbers are reduced. Bear in mind that on removal, the biofilm will inevitably go somewhere in the system.

The possibility of chunks of biofilm blocking small bore pipework will also need to be considered carefully before a bio-dispersant is used. For larger diameter pipework systems with strainers, it is likely that any biofilm will collect in the strainers and these will need to be checked and cleaned periodically after the addition of a bio-dispersant.

Product Activity Details

BV1455 Multitreat SF XTRA

On-line system cleaner for use with filtration.
  • Blend of polymers and biofilm dispersant.
  • Effectively lifts and moves organic, debris, loose iron oxide deposits and biofilm which are then removed with on-line filtration.

BV167 Oilsperse 3

Biofilm Dispersants
  • Low/non-foaming bio dispersant for use in closed circuits in conjunction with an appropriate biocide.
  • Particularly effective at removing biofilm build-up in chilled systems.


B & V Chemicals has a full range of scale and corrosion inhibitors, pre-commission cleaners, system flush chemicals, and biocides for use in closed circuit heating and chilled systems. Our range also contains many specialist products formulated for use in specific specialist or problematic situations.

For advice on the selection or use of any of the products mentioned above, please contact our technical department. We are always available to help with advice on product selection, problem solving and compatibility with other formulations already in use in particular systems.

Jill Cooper

Jill Cooper

Jill Cooper is Own Label Manager at B&V Chemicals, a leading UK and Export distributor of Water Treatment chemicals for Cooling Water Systems chemicals, Closed Circuit chemicals, Boiler chemicals, Hot and Cold Water System Chemicals, Effluent and Wastewater chemicals. A Microbiologist and Chemist, she has 20+ years production, toll blending and regulatory knowledge.

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