It is possible that storage heaters may require two separate electrical supply lines in order to function properly. The specific requirements for a storage heater will depend on the type and model of the heater, as well as the electrical system of the home.
Some storage heaters may require a separate electrical supply line for the heating element and a separate line for the control system. This can be necessary to ensure that the heater has enough power to function properly and to prevent overloading the electrical circuit.
Other storage heaters may be able to function using a single electrical supply line, depending on the size and power requirements of the heater. In these cases, it may not be necessary to have a separate supply line for the control system.