by A. Smith

Created on: December 15, 2011   Last Updated: December 17, 2011

Unlike new gas furnaces, which use electronic ignition to light the gas burner directly, older gas furnaces use a pilot light as an ignition flame to light the gas burner. The burner cannot light and the furnace will not provide heat if this standing pilot light goes out. These instructions are for lighting a furnace pilot light in furnaces which use a standing pilot light.

Natural Gas

Most newer furnaces are designed so that the natural gas feed automatically cuts off when the pilot light goes off. In these furnaces, the pilot light is supposed to go off when the furnace is not in use.

In older furnaces, the natural gas feed sometimes continues even when the pilot light is off. Most of these furnaces are more than twenty years old. In these older furnaces, natural gas may build up while the pilot light is off.

If you smell natural gas, do not attempt to relight the pilot light. Call the gas company immediately. Open the windows. Do not light an open flame or turn on an electric light.

If you do not smell natural gas, it is safe to relight the pilot light.

Relighting the Pilot Light

Most manufacturers have standard instructions on how to relight the pilot light. These instructions may be fastened directly to the furnace. They will also be in the furnace manual. Follow these instructions if you have them available.

Otherwise, find the pilot light assembly. You may need to remove an access panel.

The pilot light assembly should have a nearby gas valve with settings for on, off, and pilot. The valve is on the gas line to the furnace. If the front is sealed with glass, you have a direct vent and the gas valve is located inside a grate along the floor. Turn this valve off, wait three minutes for residual gas to clear away, then turn it to the pilot setting.

Touch a lit match to the pilot opening. If there is a reset button, push this button at the same time. Hold the button down for at least 30 seconds, until the pilot light has relit.

Some pilot openings are difficult to reach. Use a long fireplace match or a waxed splinter of wood to relight these pilot lights. You can also use a long barbecue lighter.

After the pilot light is burning steadily, turn the gas valve back to the on position. Replace the access panel if you removed it previously.

Pilot Light Problems

A pilot light which won't stay lit or which keeps blowing out indicates a problem that should be fixed. Turn off the gas valve before trying any of these solutions.

Gas pilot lights should be bright blue, with no more than a tinge of yellow. Propane pilot lights should be blue-green.

If the flame is yellow or red, there is a contamination problem. A split flame is caused by dirt in the pilot tube. Clean the opening to the pilot light with a piece of fine wire and emery cloth if needed. Do not use flammable solvents. Relight the pilot light using the previous procedure. If it stays on, this is all that is needed.

In an older furnace, the thermocouple may be the cause and should be replaced. After ruling out the thermocouple, another possible cause is a bad gas valve.

A flickering or wavering flame may be caused by a draft. A new furnace in a house on a narrow lot may have an exhaust pipe which is too short. The wind will keep blowing out the pilot light until the exhaust pipe is extended.

Gas furnaces which use electronic ignition do not have pilot lights and have no continuously burning flame. This is one of the ways of achieving higher efficiency. If the ignition system malfunctions on this kind of furnace, it should be examined by a qualified professional.

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