Late ignition problems on an oil burner furnace need to be taken very seriously. Not only could the problem lead to a dangerous explosion if the reset button is pushed too many times, but if the furnace fails when the temperature is below zero, it could make living in the house very uncomfortable. Here are a few of the common causes of late ignition on an oil burner furnace.
1 - Air leak in the Fuel Line
If the O-rings near the fuel filter are old or corroded, they may be leaking air into the fuel line. If this is the case, the fuel pump must pump the air out of the lines before it can begin pumping fuel to the igniter.
2 - Furnace May have a Pre-Purge Phase
One piece of good news is that not all delayed ignitions are signs that something is wrong. Some furnaces have a pre-purge feature that makes the unit run for up to 15 seconds before it lights. This allows the pump to build up proper pressure and draft which, in turn, ensures a smooth ignition. Pre-purge processes will always be the same length of time. So, if the length of time between activating the burner and ignition varies, then it is probably not due to this feature.
3 - Clogged Nozzle
The nozzle is the brass piece that atomizes the oil so that it will burn more quickly and efficiently. These nozzles have tiny screens within them that break up the oil into tiny droplets, but as time goes by these screens can clog up. When this happens, the amount of fuel that is able to pass through the nozzle will be reduced, possibly delaying or even preventing ignition.
4 - Dirty or Improperly Spaced Igniter Gap
Make sure that the gap on the igniter is clean and soot-free so that it can spark easily. Also, make sure the gap on the electrode of the igniter is between 1/8- and 3/16-inch wide (about the width of two pennies) to ensure an adequate spark for ignition.