What was found
L1 WINDOW OVERHEAT AT FL360 RESET WITH QRH. GROUNDED - YES. PERFORMED GVI WIRING AND VERIFIED H-RATING FOR L-1 WINDOW MATCHED TO HEAT TAP REF B737-800 WDM 30-41-11 PAGE 6 SHEET 1. INITIAL RESISTANCE CK OF PRIMARY AND ALT SENSORS @ TEMP CK GOOD @ 325 OHMS EACH (REF B737-800 AMM 30-41-21-760-801). AFTER EXTENDED RUN TIME PRIMARY L-1 WINDOW HEAT SENSOR RESISTANCE GREW TO 425 OHMS REVEALING BREAKDOWN OF PRIMARY SENSOR - SWITCHED TO ALT SENSOR.