pilot light 
noun
1A small gas burner kept alight permanently to light a larger burner when needed, especially on a gas cooker or boiler.One such standard is that all gas fireplaces have a safety pilot system and a safety combination valve, making it impossible for gas to flow to a burner until a pilot light is lit....
- She claimed that they told her that they had turned off the pilot light on the kitchen stove, turned up the burners, and would open the doors to the children's rooms if she did not cooperate.
- When an overloaded plug begins to spark or when the pilot light in a boiler ignites in a house where the gas has been left on?
2An electric indicator light or control light.Tankless heaters are available with standing pilot lights or an electronic pilot light ignition....
- After weeks without proper rest, the Needles lighthouse was mistaken for a pilot light and the Irex sailed into the since-named Irex Rock in Scratchell's Bay.
- The power supply unit features an on/off toggle switch, a red pilot light and a fuse holder.