If your furnace or boiler has a pilot light, you’ll want to know how to relight it. Newer models usually have an electronic igniter and don’t use a pilot light, but plenty of “vintage” heating equipment is still in service. In a furnace, the pilot light and the thermocouple work together to keep the gas flowing or shut the main gas valve off if a problem occurs. If the pilot light goes out or doesn’t otherwise burn well enough to keep the thermocouple hot, the thermocouple will release and the main gas valve will close. When this happens, your furnace won’t turn on.
Downdrafts – air that is forced down the chimney from the outside by a high wind – can occasionally cause a pilot light to extinguish itself. This is normal and doesn’t indicate a problem.
Lighting a pilot light is a relatively easy task. Your furnace may even have a label that provides precise directions and diagrams for your particular model. If so, follow the directions on your furnace. If not, I’ve provided general directions for lighting a pilot light.
To light a pilot light, turn your home’s thermostat down or off. (Don’t skip this step!). Some directions tell you to turn the thermostat on and up to 75 or 80 degrees. If your thermostat is on and asking for heat, your main burners will ignite as soon as you light the pilot light. If you’ve never seen the main burner on your furnace ignite, it can be a little surprising to see that much flame! Personally, I don’t like that kind of excitement, and since the thermostat and the pilot light are independent, I see no need to get the thermostat involved at this point.
You’ll need a flame source, like a match or lighter. Pilot lights aren’t known for their convenient location. You’ll want a long match or even a butane barbecue lighter for this task because you may have to get the flame deep into the furnace to get the pilot light’s attention.
Access the pilot light on the furnace. It may be behind a little door or you might have to remove side or bottom panel on the furnace to expose the pilot light assembly. You’ll have to open the pilot’s safety valve manually, usually by pressing and holding a big red button or turning a knob to the “pilot” position and holding the knob in. (It’s usually a two- or even three-handed job!) If your pilot switch has been replaced, the button may be a different color, but it will be in a pretty visible location and it will probably be the only button around.
Light the match and put it near the pilot light. Once the pilot light ignites, you’ll have to hold the safety valve open for about a minute, while the pilot light heats the thermocouple. After a minute, let go of the button. The thermocouple should be hot enough to keep the valve open by itself. If the pilot light stays lit, button up the furnace. You’re done! Turn the thermostat up to your preferred setting and warm up.
If the pilot light will not light, stay lit or the thermocouple disengages repeatedly (you’ll hear a loud “CLICK” when the thermocouple lets go), you may have a bigger problem that requires professional intervention.
When the weather turns warm in the Spring, you can extinguish the pilot light on the furnace to save a few dollars on your gas bill each month. You won’t become wealthy by doing this, but there’s no reason to waste gas, either. If you decide to do this, be sure to turn the pilot light’s gas valve to the “off” position before you shut the system down for the summer. If you have a button rather than a knob, the valve will be a little thumb valve you can turn 90° and will be located somewhere near the pilot light. If the valve isn’t obvious, follow the gas line from the pilot light to the first valve you find, and might be located outside the furnace cabinet.
We’re always on call at Boston Standard Plumbing & Heating, so even if you just need your pilot light lit, we can help. Contact us at (617) 288-2911 and we’ll be happy to lend a hand.