Narrative:

I was the pilot flying (PF) on the subject flight. After takeoff; the fire fault light intermittently flickered; flashed; and on steady passing 10;000 feet. At that point; I took both the aircraft and radios and the pilot monitoring (pm) performed the QRH. We determined that there was nothing to be done. Our fire detection system was to be considered completely or partially failed and no way to determine that extent. I sent multiple free test messages to dispatch to have them contact maintenance to see if we had overlooked anything and if there was a way to continue the flight. Maintenance wanted to verify a or B systems. That could not be done as the light was flashing and we could not catch the flash; further; that was not an inflight procedure in our approved QRH. I sent the message that we felt we were not legal to continue and a return to the departure airport was in order. Dispatch responded in agreement. During all this time; we continued to fly west and burn fuel. I felt this would lighten our ultimate overweight landing and maximize our set-up time for the return. I specifically told ATC that the fire fault light was on. The pm did the runway landing analysis. As a result of that; I elected to request and land on runway xyr just in case we had fading brakes due to the landing weight of 151;600 pounds. I briefed the flight attendants on the issue; assured them of a normal approach and landing. I also informed them that our fire detection system was in doubt and they should inform me of any visually detected fire outside the plane. I then told the passenger that we had a minor malfunction and would return. I also told them that because of the heavy landing; emergency personnel would meet the plane near the runway to ensure our brakes were cool enough to return to the gate. We briefed and flew the ILS to xyr landing with flaps 30 and brakes 3. Airport rescue and fire fighting (arff) verified on the discreet frequency that our brake temperature was safe for a return to the gate. Flight was terminated without further incident.

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Original NASA ASRS Text

Title: B737-800 flight crew reported the Engine Fire/Overheat Detector Fault Light illuminated in climb; resulting in a return to the departure airport.

Narrative: I was the Pilot Flying (PF) on the subject flight. After takeoff; the Fire Fault Light intermittently flickered; flashed; and on steady passing 10;000 feet. At that point; I took both the aircraft and radios and the Pilot Monitoring (PM) performed the QRH. We determined that there was nothing to be done. Our Fire Detection System was to be considered completely or partially failed and no way to determine that extent. I sent multiple free test messages to dispatch to have them contact Maintenance to see if we had overlooked anything and if there was a way to continue the flight. Maintenance wanted to verify A or B systems. That could not be done as the light was flashing and we could not catch the flash; further; that was not an inflight procedure in our approved QRH. I sent the message that we felt we were not legal to continue and a return to the departure airport was in order. Dispatch responded in agreement. During all this time; we continued to fly west and burn fuel. I felt this would lighten our ultimate overweight landing and maximize our set-up time for the return. I specifically told ATC that the Fire Fault Light was on. The PM did the runway landing analysis. As a result of that; I elected to request and land on runway XYR just in case we had fading brakes due to the landing weight of 151;600 pounds. I briefed the flight attendants on the issue; assured them of a normal approach and landing. I also informed them that our fire detection system was in doubt and they should inform me of any visually detected fire outside the plane. I then told the passenger that we had a minor malfunction and would return. I also told them that because of the heavy landing; emergency personnel would meet the plane near the runway to ensure our brakes were cool enough to return to the gate. We briefed and flew the ILS to XYR landing with flaps 30 and brakes 3. Airport Rescue and Fire Fighting (ARFF) verified on the discreet frequency that our brake temperature was safe for a return to the gate. Flight was terminated without further incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.