A coolant storage tank (1) for storing coolant in a fuel cell system (2), the coolant storage tank comprising a plurality of individually controllable heater elements (7, 8a, 8b). A coolant storage tank comprising a first heater element (7) located at a base of the coolant storage tank and a second heater element (8a) is also disclosed. A coolant storage tank comprising a first coolant storage compartment (50) in fluid communication with a second coolant storage compartment (51), the first coolant storage compartment including at least a first heater element (54) and wherein the second coolant storage compartment is unheated is also disclosed. A method of melting frozen coolant in a coolant storage tank is also disclosed.