DIY Appliance Repair: How to Test an Oil Furnace Electronic Spark Generator
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DIY Appliance Repair: How to Test an Oil Furnace Electronic Spark Generator

Just as the electronic ignition have replaced the old pilot light systems on gas ranges and oven/broilers, so has the electronic spark generators replaced the older conventional High-Voltage transformers on residential oil-fired furnaces. The electronic spark generators have many advantages over the old conventional HV Transformers. The electronic spark generator generate a hotter spark which ignites and burns more of the fuel oil as it is sprayed from the nozzle, which means conserving natural resources and lowering your heating bills. They are also more reliable, lighter in weight, and less bulky than the old iron core transformers.

The Electronic Spark Generators are completely solid-state devices that rectify the 120 Volts Alternating Current (AC) into 120 Volts Direct Current (DC).


The rectified AC is then used to trigger power transistor on and off at a rate of 15,000 to 30,000 times per second. Their pulsating collector current is then sent to the primary winding of a small transformer that is part of the electronic spark generator. The secondary winding of this special high-frequency, high-voltage step-up transformer produces an output voltage of 14,000 volts which also pulses at between 15,000 and 30,000 times per second. This high-frequency current produces a very intensely hot spark at the electrodes.

A Bolt-In replacement for a Conventional HV Transformer.

If your old oil burner High-Voltage transformer is in need of replacement, you should consider replacing it with a solid-state Electronic Spark Generator.


The electronic spark generator units are available with a wide variety of base plate adapters so they bolt right in where the old conventional HV transformer mounted. Everything that you will need comes in a service kit that looks like this.

Tools and test equipment needed.

  • Digital Multimeter (DMM)

  • Screwdrivers

  • Long-Nose Pliers

  • Set of Nut Drivers or a 1/4-Inch Drive Socket Set

  • 120-Volt, 3-Wire Service Jumper with Alligator Clips

Testing the Electronic Spark Generator with a High-Voltage Probe

  • Turn off the power going to the furnace at the main service panel. As an added safety precaution, also turn off the oil furnace's emergency disconnect switch. The Emergency disconnect switch will be somewhere withing site of the furnace and have a Red switch cover plate. Except for its Red cover plate, the switch itself will look like a regular light switch.

  • Remove the Electronic Spark generator from the furnace for easier inspection and testing. Wipe off the porcelain high-voltage insulators and check them for signs of cracks or other damage. Replace the module if the insulators are damaged in any manner.

  • Connect the Black and White insulated alligator clips of the service jumper to the modules primary leads. Connect the green insulated or uninsulated alligator clip to the modules metal base plate.

  • Plug the service cord into a 120 -Volt receptacle. Using a well insulated screwdriver, short between the two high voltage terminals. Slowly move the screwdriver back from the second terminal. If the module is good, you should be able to draw out a 3/4-inch long spark.

  • As a secondary check of the spark generators viability, disconnect the service cord and take an Ohms reading between each of the high-voltage terminals and its metal base-plate. A good module will have an Ohms reading of less than 2000 Ohms between the high-voltage terminals and the grounded base-plate. If the two reading differ by more than 20 percent, the module is defective and should be replaced.

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Comments (6)

Very well presented.

Jerry, you are a genious.  I am finding all of these DIY articles extremely useful.

Very interesting and informative, as always.

Re-visiting. The photos are not showing for this article except the main one. I've had this problem with some of my articles as well.

Lost the photos. Interesting. I've put them back in. Thanks for the heads up, Bethany.

In this modren world people are using electronics for making their lifes easier but people dont have awareness that how they can use electroincs in proper way. After reading your articles all of us getting good knoledge about different electronics. I would like to thank you for sharing so many products in your articles. Keep writing. Excellent work once again.