Most gas boiler furnaces use an electronic ignition system. There are 2 different types of electronic ignition systems: electronic spark or glow plugs. The ignition system works by creating a spark or heat to light the pilot. The electronic system works by the same idea of manual lighting the pilot on an older standing pilot furnace. If the burner on your furnace will not light, the spark may need to be replaced. When working with a gas boiler it is best to consult a professional. Working with natural gas can be very dangerous and can result in injury if not done properly.
Step 1: Preparation
Turn off natural gas supply. Once the gas supply is disconnected allow a few minutes for gas to dissipate before starting removal of spark plugs. It may be best to contact the gas company for proper instruction on how to turn off gas supply. Locate the manual for the boiler. In most cases there will be a labeled diagram printed on the boiler. If a manual or diagram can't be found, contact the manufacturer for a replacement. The diagram will show the location of the spark plugs.
Step 2: Spark Plug Removal
Remove access panel where spark plugs are located using a screwdriver. Once removed place panel and screws aside to be replaced once project is complete. The spark plugs should be located behind the access panel. The space where the spark plugs are located may be very tight and hard to see or reach. Use an adjustable arm mirror if needed to locate the spark plugs. Once the plugs are located, use the proper size socket wrench to remove the old spark plugs. Once removed make note of the gauge of the gap to assist in installation of the new plugs.
Step 3: Installation of Spark Plugs
Remove the new spark plugs from the packaging. Use the spark plug gauge to gap the new plugs to the proper size. The correct gauge will be found on the packaging. Compare this measurement to the gauge on the old spark plugs. If the old plugs were not gapped correctly this may have been the cause of the original problem. Using the socket wrench, install the new plugs. Check to insure the plugs are installed correctly and are secure. Use the mirror if needed to check all sides of the plug before replacing the access panel door.
Step 4: Testing the Furnace
Reattach the access panel using a screwdriver. Reconnect the gas supply to the boiler and turn on the gas supply. Before powering on the boiler, wait at least 10 minutes and inspect the area for signs and smell of a gas leak. If no leak is detected, power-on the furnace. The burner should light and the furnace should function properly. If changing the spark plugs doesn't correct the problem, contact a professional to troubleshoot and complete the repair.