It is a requirement of ACOP L8 that on an annual basis there should be a;
‘visual check on internal surfaces of calorifiers for scale and sludge, cleaning if necessary’.
L8 also requires that domestic hot water should be heated to 60°C at source (the hot water calorifier) to ensure that any bacteria are thermally eradicated and this gives the water a chance to reach the supplied outlets at a minimum of 50°C avoiding the temperature range supporting bacterial growth again, as required by L8.
With Legionella control relying so heavily on the maintenance of a strict temperature control regime it is essential that the system is capable of reaching and maintaining the required levels and coping with demand (recovery rate).
Scale can have a dramatic effect on the ability of a calorifier to heat /distribute hot water and provides essential nutrients for bacterial growth. In hard water areas it can take only a matter of months for scale to coat the element / heat exchangers, the inside of pipework and pumps drastically reducing efficiency. We have even known scale to block the cold water feed to a cylinder installed only 6 months previously! The reduction in efficiency also has the inevitable consequence of putting up energy bills, up to 25% – something we could all do without at the moment.
It is therefore a good idea to de scale your hot water cylinder when deemed necessary, not only to comply with ACOP L8, but also to keep fuel bills to a minimum. There are two main ways of getting rid of scale; physically or chemically though usually a combination of the two is preferable.
For a large number of new calorifiers there is no means of physical entry and so using chemicals is the only options. Larger cylinders and older styles are often installed with inspection hatches and the bulk of the scale can be removed manually – this reduces the amount of chemical de scaling required and can speed up the process.
Chemical de scaling involves introducing an acid based substance to the cylinder to dissolve the scale, generally resulting in the production of carbon dioxide. The speed of the reaction is affected by temperature so it is common for the chemical to be added, the cylinder heated up and left for several hours.
Ultimately, the method used will depend on accessibility of the cylinder, the amount of scale, disruption and the set up of the water system. Prevention is always better than cure so consideration should be given to installing a water softener!