Although propane water heaters, room heaters, and furnaces are usually equipped with electronic ignition devices, many still rely on a pilot light. The pilot is a small flame that burns continuously and is positioned strategically to light the main burner when the gas valve is switched on. When the pilot light goes out, the burner won't function. So if the pilot begins to flicker, it's important to determine the cause, and address it.
Empty Tank
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Utility companies supply natural gas through service lines that originate at their offices, but that isn't the case with propane. An independent supplier delivers it and pumps it into a holding tank. If the supplier isn't contracted to regularly check and refill the tank, the propane supply can dwindle surprisingly quickly. A typical residential tank holds 500 gallons, and although the tank appears large, its contents may last only a few months in winter. As the tank empties, the pilot lights will flicker on all the appliances that are connected. The pilot lights will go out if the tank isn't refilled.
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Dirt in the Pilot Tube
The tubing that supplies the pilot light is narrow and susceptible to clogging. When an obstruction inhibits gas flow, the flame may appear anemic or may split in two. Appliances that have a standing pilot flame are usually old, and have been in service long enough to have collected debris or corroded metal around the opening of the pilot tube or inside the tube. Since the tube is removable with a small wrench, it is possible to clean it out by spraying into it with a canister of compressed air. Always turn off the gas valve before you disassemble the pilot tube.
Air Flow
The pilot light needs air to burn, but not too much nor too little. Too much air, in the form of a draft, will cause the pilot to flicker and may blow it out. The draft may be coming from under a door or through a poorly-sealed window, or the draft may be intermittent, occurring only when a door or window is open. Too little air will also cause the pilot light to burn weakly and flicker. A flame that is mostly yellow instead of bluish with a yellow tip signifies that the pilot isn't getting enough air, or that the air isn't circulating because of a blocked vent.
Defective Thermocouple
The thermocouple is a heat-sensitive device that sends a small electric current to the gas valve, signaling it to remain open so the pilot will keep burning. If the thermocouple is defective, the gas supply to the pilot may be intermittent, causing it to flicker. This may also happen if the thermocouple is too far away from the pilot light. The distance between the pilot and the thermocouple can usually be adjusted with a screwdriver, as can the height of the pilot flame. If neither adjustment produces a steady flame, replace the old thermocouple with a new one.