Information

Biological Contamination in Central Heating Systems

Feed & Expansion Systems

Leathery skins or films of "algae" are sometimes found on the surface of expansion Systems. Generally these films are caused by fungal mould growths of, for example, Penicillium ssp. rather than algae. The latter require light to grow like all other plants.

The slime film may smell foul but provided it does not enter the pipe-work it will cause few problems. If the system is drained for any reason, such as removal of radiators during decorating, this can result in the debris being drawn into the system where it may cause blockages. Such blockages are very substantive and even hard flushing with water may not be an entirely satisfactory means of removal.

Fungal slimes usually result from the expansion System not being properly covered or there being too low a dose of corrosion inhibitor in the tank itself to maintain sterility. Dust, insects and spores can enter the System from the environment and even if a biocide is present in the inhibitor continuous ingress over a prolonged period may exhaust this. If the inhibitor is added to the system whilst it is being filled this results in all of the product passing into the pipe-work and radiators with little or nothing in the System. Although the inhibitor will eventually intermix with the water throughout the system, before this can occur there is an opportunity for microbiological growth to be established and these growths may then be able to tolerate the slow ingress of biocide from the treatment as the water mixes.

ACTION: B0ilout the System and disinfect. Refill the tank and top up the inhibitor concentration.  

Within the entire system

The formation of flammable gas within a system which is correctly treated with an inhibitor may indicate that microbiological fermentation is taking place. The gas is likely to be present in all radiators. This contrasts with air ingress which typically accumulate in just one radiator. Methane (burns with a blue flame) is most often found but should not be confused with hydrogen evolution resulting from corrosion. Hydrogen sulphide (bad egg smell) may also be found and this is associated with the presence of Sulphate Reducing Bacteria (SRB's) which cause corrosion.

Bacterial or yeast infestations may arise from organisms entering the system from the supply water, from commissioning debris in new systems and from ingress from the atmosphere into open expansion Systems of older systems in particular.

ACTION: Addition biocide should control microbiological growths and prevent gas formation. Where the contamination is heavy several repeat doses of biocide may be required and in such situation it may be advantageous to drain the system and retreat the system.