If you are mostly familiar with older gas appliances, then it's likely that one of the first things you think of is the pilot light. The purpose of this tiny component is to keep a flame burning (literally) that can be used to ignite the natural gas when the furnace is running. Because of the importance of the pilot light, many people immediately assume that there is a problem with their pilot light if the furnace won't light. It is so common for pilot lights to go out that furnaces and other gas appliances usually have instructions for relighting the pilot light printed directly on the unit.
All of this points to the pilot light as being the most likely cause of an ignition problem, right? It can seem that way, except for one small problem: most modern furnaces are not equipped with pilot lights.
If you do have an older furnace with a pilot light, then a failure to ignite can very well be caused by your pilot light being out. Pilot lights were replaced because they are both inefficient and problematic. Since your pilot light is constantly burning, it requires a constant supply of natural gas even when the furnace is not on. This usually only costs a few dollars per month, but it can add up over time in addition to being a major waste of environmental resources on a wide scale.
Even worse for homeowners, pilot lights are prone to a variety of problems. They can blow out very easily, leading to a surprising lack of heat when you turn up your thermostat in the winter. The pilot light tubes can also become clogged, preventing the light from relighting or starving it of gas. All of these issues have led to gas appliances replacing their pilot lights with electronic ignition systems.
Electricity to the Rescue
Electronic ignition systems are fairly straightforward in their operation and they largely solve the problems inherent to pilot lights. If your furnace is equipped with an electric ignition, then it uses a spark to ignite the burner when necessary. This means that your furnace isn't using any gas when it isn't running, allowing it to be drastically more efficient over the long run. Electric ignition systems are also not prone to blowing out (since there is no flame) and there is no gas supply tube to become clogged.
Failure to Zap
Unfortunately, electronic ignition systems do not last forever either. In fact, you'll likely need to replace your igniter at least once over the life of the furnace. Symptoms of a failing igniter are usually fairly obvious, however, and repairing or replacing one is generally not expensive. As your igniter begins to wear out, you will likely notice your furnace cycling on and off more often until eventually it won't turn on at all. If your thermostat is turned up and the furnace does not seem to ignite at all, then there is a good chance that your electronic ignition is in need of attention.
Check out professional heating services in your area if you would like more information.