Abstract: The invention relates to a method for determining the amount of warm water in a water tank of domestic water heating system, which includes: (a) Pre-determining various situation graphs, each graph describes the variation of the water temperature in said water tank as a function of time, in one specific operational situation of the system; (b) Dividing each of said graphs to plurality of sections, each graph section describes the variation of the water temperature in the water tank as a function of time, during a sectional period of time; (c) Determining for each graph section the percentage of warm water in the tank at the end of said section; (d) Storing in a memory storage said plurality of graph sections, and the corresponding percentage of warm water in the tank at the end of said section, as determined; (e) During the operation of the heating system, sampling periodically the temperature in the tank; (f) For each present sequence of samples, finding in said memory storage the most similar graph section,

Abstract: Method for determining the amount of warm water in a water tank, comprising: pre-determining various situation graphs, each graph describing the variation of the water temperature as a function of time, in one specific operational situation of the system; dividing each of said graphs in a plurality of sections; determining for each graph section the percentage of warm water in the tank; storing in a memory said graph sections, and the corresponding percentage of warm water in the tank; during the operation of the heating system, sampling periodically the. temperature in the tank; for each sequence of samples, finding the most similar graph section, and the percentage of warm water that corresponds to said graph section; and displaying to the user said present percentage of warm water in the tank.