The HT-heater is a unit which distinguishes itself by a clear design and high efficiency. It will perform its functions perfectly during years, as long as the inspections, revisions, cleaning, etc., specified hereafter, are carried out reliably. Inspection and revision should only be executed by reliable and skilled personnel. Observations made during inspection as well as the revision works carried out have to be entered in the heater log book. These notes will give the user relevant information about the condition of the heater.