VIESSMANN Vitodens 100-35 A few hours ago (about three) the expansion vessel was replaced. The pressure, already adjusted, has dropped from 1.5 to 1.2. (before it fell to 0 in twelve hours or less). I have checked the water meter: it does not move, nor has it moved in that time. Can, despite this, exist enough leakage to lower the pressure? . From how much water loss pressure drop occurs). Thanks in advance I reduce the question to the following: What damage can occur in the boiler by working at a pressure of only 1 versus 1.5? Closing keys I have isolated the boiler circuit, resetting the pressure again to 1.5: after about 24 hours it has only dropped to 1.4. I deduce that the circuit has been well purged and that the pressure loss is probably due to the heating circuit. (As I said at the beginning, the accountant of water does not manifest losses). Should I focus on radiators? On the other hand, if at lower pressure less wear and, as I imagine, what flow or temperature will depend on it, what would be the optimum pressure? The one recommended by the manufacturer? Thank you so much for the comments . They are giving me ideas to form a criterion.