Technical definition
Boron is a measurement of the concentration of elemental boron present in dissolved boron-containing species within the heating system water, expressed in milligrams per litre (mg/L).
In water, boron is typically present as boric acid and/or borate species, with the balance between these forms influenced by pH. Borate compounds may be associated with some water-treatment formulations, where they can contribute to pH buffering and corrosion-control chemistry. Research on aqueous metal systems also demonstrates that borate environments can influence the passivation and corrosion behaviour of steel.
Within Fernox laboratory water analysis, Boron is treated as a treatment-dependent parameter rather than having one universal acceptable concentration. Fernox's published laboratory data lists the recommended Boron level as “Depends on treatment.”
Simplified definition
Boron measures the amount of boron-containing substances present in the heating system water.
Boron may come from the original filling water or from certain heating-system treatment chemicals. Measuring it can therefore help build a picture of how the system has been treated and identify unexpected changes in the water chemistry.
Boron is useful primarily as a treatment and water-chemistry indicator rather than as a direct measurement of corrosion or scale.
An abnormal or unexpected Boron result may indicate:
Boron naturally present in the original filling water.
The presence of a borate-containing treatment product.
Changes in the concentration of a treatment chemical.
Dilution of treated system water through draining, leakage or repeated topping-up.
Introduction of a different water or chemical source.
Residual treatment or cleaning chemicals within the system.
Changes in system chemistry following flushing, refilling or maintenance.
Contamination from an unexpected source.
Where borates form part of a treatment formulation, they can contribute to the chemical environment used to control corrosion and maintain suitable water conditions. Studies of carbon steel in borate solutions show that borate concentration can influence metal passivation and electrochemical behaviour.
Boron testing can therefore help:
Establish a more complete chemical fingerprint of the system water.
Compare circulating system water with the original filling water.
Identify the possible presence of borate-containing treatment chemistry.
Detect dilution or significant changes in a known treatment regime.
Support interpretation of unusual pH, alkalinity or conductivity results.
Help determine whether the system chemistry is consistent with the products known to have been added.
Boron can be particularly useful when considered alongside other treatment-related parameters, such as Molybdate, Phosphorus, Sodium, Potassium and Silicates. Together, these measurements can provide considerably more information about the system's treatment history than any one parameter alone.
Boron should not normally be assessed in isolation, and an elevated Boron result does not automatically indicate a problem with the heating system.
Unlike parameters such as Iron or Copper, Boron is not primarily a corrosion-product measurement. Similarly, it is not a hardness parameter like Calcium or Magnesium. Its significance depends largely on the filling water and treatment chemistry present within the system.
This is particularly important for the Fernox App because Fernox laboratory data identifies the recommended Boron level as “Depends on treatment”, rather than specifying a single pass/fail concentration.
A higher Boron concentration may therefore be completely expected in a system containing a boron- or borate-containing treatment product. Conversely, an unexplained change in Boron compared with the filling water or previous test results may provide useful evidence that the system's water chemistry has changed.
The result should therefore be assessed against the original filling-water Boron concentration, known treatment products, previous test results, pH, alkalinity, conductivity and other treatment-related parameters.
