Seller warrants equipment and parts manufactured by it and supplied thereunder to be free from defects in materials and workmanship for a period of one year after shipment, self regulating heating cables are to be free from defects in materials and workmanship for a period of two years after shipment. If, within such period, any such equipment or parts shall be proved to Seller’s satisfaction to be defective, such equipment or parts shall, at Seller’s option, be repaired or replaced by Seller, for installation at Buyer’s expense. Seller’s obligation hereunder shall be limited to such repair and replacement, F.O.B. its factory, and shall be conditioned upon Seller’s receiving written notice of any alleged defect within ten (10) days after its discovery and at Seller’s option, return of such equipment or parts prepaid to its factory.