Corrosion is generally caused by the presence of oxygen, but can also be brought about by galvanic effects which occur when different metals are connected. Aluminium is especially prone, and for this reason should never be connected directly to copper or brass.

When corrosion occurs, black magnetite is formed which can restrict circulation in radiators, cause premature pump failure, and form deposits in heat exchangers which manifest themselves in boiler noise and lost efficiency.

Gassing

Another side-effect of corrosion, requires radiators to be bled in order to restore circulation.

Pin-hole corrosion

Can give rise to alarmingly rapid perforation and loss of radiators. It is normally due to over-use of flux and lack of effective flushing in new systems.

Scale

The problem of scale varies considerably across the country depending on the water supply. In hard water areas such as the East and South East of England, scaling is especially severe due to the high lime content in the water. Lime gives rise to rapid 'furring' of the heat exchanger where it causes two major problems - noise and increased fuel usage.

In modern boilers the effect of scale on boiler efficiency and fuel usage is dramatic. An egg-shell thickness of scale can increase fuel consumption by as much as

Scale often gives rise to boiler noise commonly known as 'kettling'. This can be an extreme nuisance to the householder who has to put up with banging noises which can be heard all over the house.

Microbiological Growth

Frequently open to the air from their position in the loft, feed and expansion cisterns are prone to contamination from all sorts of micro-organisms such as bacteria and fungi. Once in the cistern, they can breed and give rise to unpleasant growths and slimes which can foul the heating system and cause blockages and deposits.