As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
R2 WINDOW HEAT OVERHEAT LIGHT CAME ON ABOUT 1.5 HRS INTO FLIGHT. RAN AND TURN OFF HEAT FOR 5 MINUTES AND TURN BACK ON. LIGHT REMAINED OFF FOR THE DURATION 4 HOURS FLIGHT WINDOW WAS ON SHADE SIDE OF AIRCRAFT. GROUNDED - YES. PERFORMED BITE TEST ON R2 WINDOW HEAT OVERHEAT PER B737-900 AMM 30-41-11-710-801, NO FAULT NOTED. OK FOR SERVICE.