Hello Leonardo. In my experience, when a water heater does not heat up, the first thing to check is the gas pressure. If you do not have a pressure gauge, light the large kitchen burner and then the water heater. If the kitchen flame is reduced, the gas pressure is insufficient. Are you sure your team is Ursus and not Albin Trotter? The membranes of these albin, if they are not perforated or about to break, are not the cause of the problem. An important detail is that this model requires excellent water pressure, always over 2 bar, otherwise the membrane does not complete its travel, that is to say it does not reach its maximum capacity and unfortunately it lacks any adjustment in that regard. Check the output flow, which does not exceed 12 l / min. or lower than 7, as this could indicate insufficient pressure (this time of water) or a restriction in the passage either before or after the heater (eg dirty filter or aerator, "ecological" water-saving shower) . In short, if there is a lack of temperature, it is almost never the fault of the water heater. Greetings.