Water-scale precipitation was observed on electrical heaters within boilers for hot water preparation within households. Different permanent magnetic devices and electromagnetic device were installed on the inlet pipe in the boiler. The system was supplied with tap water of known chemical composition. The magnetic water treatment took place over several days under constant conditions (temperature in the boiler, water composition, etc.) along two parallel lines. The first one was the treated line and the second was for comparison. This paper presents the experimentally confirmed results using different permanent magnets and electromagnets for reducing the amount of precipitated water-scale on heaters for hot water. The impacts of different operational conditions are presented regarding the devices' effectiveness. Scale samples were analysed by X-ray diffraction, where it was discovered that all the samples were in the shapes of aragonite. (C) 2014 Elsevier Ltd. All rights reserved.