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Combustion heater overheat switch reset

Aviation Mechanic Airframe (AMA) practice question 10 of 15 on Environmental Systems. ACS element AM.II.G.R5 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA combustion heater's overheat switch has activated and shut the heater down. What must happen before the heater can be operated again?

  1. AThe heater must cool for 15 minutes.
  2. BMaintenance must find the cause.
  3. CThe thermostat must be reset in flight.
Show the answer and explanation

Correct answer: B. Maintenance must find the cause.

  • A — incorrect No cooling period restores the heater to service; the shutdown is latched until the cause is investigated.
  • B — correct After an overheat switch activates, a flight deck light illuminates and the heater cannot be restarted until maintenance determines the cause.
  • C — incorrect The thermostat only cycles the fuel control solenoid for normal temperature control and does not clear an overheat shutdown.

BACKGROUND

Automatic controls prevent a combustion heater from operating when dangerous conditions exist. A duct limit switch cuts off fuel when there is not enough airflow to keep the heater duct below a preset temperature, a condition usually caused by a lack of ventilating airflow. An overheat switch, set at a higher temperature than the duct limit switch, guards against overheat of any kind and is designed to cut fuel to the heater before an unwanted fire occurs. When this switch activates, a light is illuminated in the flight deck and the heater cannot be restarted until maintenance determines the cause. Some heaters also contain a circuit that prevents fuel from reaching the combustion chamber if the ignition system is not working.

STUDY TIP

Treat an overheat shutdown as a troubleshooting task, not a reset: find why airflow or temperature went out of limits before restoring the heater. Follow both the aircraft and the heater manufacturer's inspection intervals and time between overhauls.

KEY POINTS

  • An activated overheat switch latches the heater off until maintenance finds the cause.
  • A duct limit switch cuts fuel when ventilating airflow is insufficient.
  • A flight deck light annunciates the overheat shutdown.

SOURCES

  • sources/ama-airframe/ch16.txt "Combustion Heaters — Safety Features"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.