The front seat heaters eventually die (wire breaks). The wires can *sometimes* be repaired, but success is variable. The sure way is to replace the elements with new ones. PNs are 4A0963555F for the bottom and 557F for the back, as shown here for leather sport seats:
The harness for the front and rear heated seats (for interest sake) looks like this:
Tom M (4Driver4) did a great heater element R&R DIY, found here: