I guess you could short the contacts of the switch temporarily, to see if it makes a difference. If it does, you at least know the switch is bad and can replace it. If not, no need to waste money
edit: description of function:
The front seats may be optionally fitted with a special heating system (consisting of two heater elements located in the cushion and squab): these heat the seat to ease the discomfort of entering a cold passenger compartment in very cold weather, e.g. when the car is left outside for long periods during winter.
The heating device located in each seat consists of two resistors operated by a switch located on the outside of each seat.
Once a certain temperature is reached, the heating action is automatically cut off by a thermal contact inside the device.
An LED located on the button itself indicates when the resistors are switched on.
The circuit is controlled by the services relay and is protected by a specific fuse, both located in the unit under the dashboard. The heating is switched on both when the ignition is on and when the ignition is off.
With the ignition on during starting, this relay is temporarily deactivated.
With the ignition off, the Body Computer keeps the relay activated - which also supplies the door mirrors and electric windows - for 3 minutes, but deactivates it immediately when one of the two front doors is opened.
The switching on of the resistors is disabled if the battery voltage is less than 10 V.