How can an expansion tank be checked for signs of waterlogging?

Begin by ensuring the system is off and the temperature has cooled. Relieve pressure by opening a nearby drain valve or air vent. Use a pressure gauge on the Schrader valve to check the air charge. A low or zero reading may indicate the tank is filled with water. A tap test using a non-metallic object can also help. If the tank sounds solid throughout, it may be waterlogged and require draining and recharging.