An expansion tank comprising a bladder style water storage tank and method of use. The expansion tank includes an alarm module to sense a flooded tank condition. The system also has the ability to sense a bladder over-extended condition. The expansion tank use includes a sonic alarm and/or a visual alarm and is used in combination with a boiler or related hot water system. Method steps using the described design are also included. The hydro-pneumatic expansion tank has important utility in HVAC, boiler and potable water systems.