Definition
A temperature-sensitive electrical switch that automatically opens or closes a circuit when a preset temperature is reached. In a combustion heater installation, the thermal switch shuts the heater off if internal temperatures exceed safe limits, protecting the aircraft from overheat and fire.
Plain English
A switch that reacts to heat. When things get too hot, it cuts the power off by itself, without the pilot having to do anything.
Context Anchor
Seen in combustion heater descriptions, heater inspection, and troubleshooting of cabin heat systems.
Derivation
Thermal comes from the Greek therme, meaning heat. So a thermal switch is simply a heat-triggered switch — one that responds to temperature rather than to a manual action.
Why Pilots Care
It automatically stops the heater before overheating can cause a fire or damage to the aircraft.
Intuition Check
Do not picture this as the normal cabin heat switch the pilot turns on and off. In this context, a thermal switch is an automatic safety device that responds to heat inside the heater system.
Example Sentence 1
If the combustion heater overheats, the thermal switch will shut it down and the cabin heat will stop working.
Example Sentence 2
After landing, the pilot reset the thermal switch following an overheat indication during the flight.