There's water, and there's water. This simple truism becomes critical when your heating system needs to be topped off with water. In extreme cases, carelessly using drinking water may ruin your boiler. TÜV SÜD's experts offer background information and practical tips.

The material: Today's heating systems are manufactured using materials of increasingly high quality - and low thickness. If heating systems are filled using household drinking water which has a high percentage of lime (calcium carbonate), deposits may form at exposed points of radiator components - in direct contact with the heat source - and may generate such extreme thermal stress that the boiler develops cracks, resulting in a leaking boiler. Another combination to avoid is water with excessive potassium levels, plus heat exchangers made of aluminium or aluminium alloys. Here the water may also chemically attack the material.

Water quality: If the heating system needs to be filled up with water, it is always wise to read the operating manual and consult the maintenance company.

Required water volume: When pressure drops in the heating system, it must be filled with water. The pressure loss is generally shown by a manometer. TÜV SÜD advises that a heating system operating normally in a detached house loses one to two liters of heating water per year through evaporation at seals and screw fittings. If more water is lost, there is generally a technical cause - perhaps a leaking pipe connection. To avoid the problems described above in filling the system with hard water, it is best to ask a specialist to check both system pressure and heating water quality during the annual maintenance inspection.  After checking the system for leaks, suitable water, if necessary with chemical additives, should be used to fill the system. To prevent corrosion, heating water should be strongly alkaline, with a pH value of over 8.5, and as free of lime as possible. By way of comparison, drinking water is neutral, with a pH value of around 7, and contains an average of 0.2 grams of lime per liter.

For more information, contact:
Dr. Thomas Oberst
Telephone: +49 (0) 89 / 57 91-23 72
Fax: +49 (0) 89 / 57 91-212
Email: thomas.oberst@tuev-sued.de
Internet: www.tuev-sued.de