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Originally Posted by: Gene  Sam, Originally Posted by: Gene
If you look closely at a finger of burner flame you will see that it is clearly made up of three separate elements:
1. Inner fuel rich cone
2. Ionized blue outer cone with current carrying capabilities
3. Outer air rich mantle.
When gas combined with air, burned energy is released in the form of heat and light. When the gas / air mixture is controlled, the outer blue cone will actually carry electrical current similar to a wire.
If we place a metal probe into this “Ionized Plume” and apply a voltage between it and the burner, current will flow. An important characteristic of a burner/flame/electrode assembly is its ability to mainly pass current in one direction. It behaves as a one way valve or rectifier.
Flame rectification systems make use of this directional characteristic when detecting a good flame to distinguish it from leakage currents that can arise due to moisture contamination, soiled igniter tip, poorly grounded burner spreader ring / burner head, cracked igniter insulation or poor house ground.
An AC voltage is applied to the electrode from the spark module and the resultant current flow which is greater in one direction than the other, is electronically detected. This current is very small, about one microamp.
The accurate placing of the electrode in the flame is important. This igniter tip needs to be perfectly located in the ionized outer blue cone to effectively send and then detect current flow. To break it down further, the spark module acts as a simple capacitor. It saves voltage like a sponge until it can hold no more. It will save and release this voltage approximately 3 times per second. When the voltage is released it follows the spark wire until reaches the spark electrode tip. The built up voltage wants to leave the tip and move to the point of least resistance. In a healthy situation this will be the burner. From the burner the voltage flow will pass through the burner head, burner tube, chassis and to ground. An interruption of this current path will cause the spark system to misbehave.
The flame also plays a very important role in this process. Because the flame is conductive, it allows the voltage to pass through its body like a bridge to the burner. This bridge allows the built up spark voltage to bleed off of the igniter tip and move to ground more easily. The resultant ionized flame bridge has now become the path of least resistance for the spark to take across the gap between the spark electrode and the burner body.
By bleeding off the buildup of voltage we stop the spark from occurring. The spark is, in effect, still there, you just canʼt see it.
Possible Causes of Continuous Sparking:
Defective spark wires.
Continuous high heat can cause spark wires to degrade. Use volt/ohm meter to determine continuity of spark wires. Look for obvious cuts/abrasions or pinch points. A defective wire can allow spark voltage to transfer through insulation to ground prior to reaching spark electrode. Under normal circumstances all igniters fire together and if the burner in question has found an easier ground path the spark will go there. It will not, however, in most cases have found a continuous ground path such as what the flame would provide under normal circumstances. This will cause the spark module to re-ignite.
Cracked Ceramic Spark Electrode
Itʼs important to determine whether the spark electrode is faulty. Physical impacts and high heat can cause the ceramic post to fracture or crack. If this occurs the spark can shoot through the ceramic insulation and will normally go to ground on the burner head rather than through the flame
/burner.
Faulty Burner Grounding
From the spark electrode / burner to earth ground it is important that you have a strong connection. This can be interrupted in many different ways.
1. Soiled spark electrode
2. Soiled burner
3. Soiled burner head
4. Corrosion between the burner head and burner tube.
Normally this will appear as a brownish stain and can be easily cleaned with a small wire brush.
Any of these conditions can interrupt current flow. It is recommended frequent cleaning with a stiff plastic or soft wire bristle brush using pure alcohol or a window cleaning solution that contains alcohol. It is commonly thought that simple igniter cleaning is enough, it is not. You have to clean all three conductive components to ensure good continuity. A small amount of grease or oil can act as an insulator and prevent the spark from flowing properly.
It is common to find one or a series of burners that will only spark occasionally. As with the previously described scenarios check all possible ground faults. This is the number one cause of erratic sparking, not spark modules as is more commonly thought. If you have made certain that
you have a strong flame current / flame placement / solid ground, replace spark module.
Gene.
I have a 6-burner natural gas Viking cook top model VGSU 160 or VGSU 161 which began to spark even after a burner lit a few months after purchase. A present, 8 years later, only one of the six burners will stop sparking when a flame is established. When one burner control is turned on, all burner igniters spark. I have a question about both the theory explained above, and about my failure to fix the continued sparking problem.Theory The wiring diagram in the installation instructions shows six burner control switches wired to six different terminals on the spark module, and an additional six terminals wired to the six spark gaps at the burners. Since there appear to be six separate circuits, I am puzzled why all six burners spark when any one control is turned on. On the other hand, if the high voltage output of the spark module is common to all six spark electrodes (within the module), and the ionized portion of a flame effectively shorts the electrode to ground, as explained by Gene above, why would turning on a second burner cause the all the electrodes to begin sparking again? Wouldn’t the existing flame continue to divert the current to ground?PracticeOn one of the five always-sparking burners I carefully cleaned the igniter and its (uncracked) insulator. Using wire brushes and emery paper I also made sure that the surface of the burner ring (which is the source of the many flamelets) was conductive in the vicinity of the igniter electrode and that the ring made good electrical contact with the base on which it rests. This conductivity was verified with an ohmmeter. Notwithstanding this effort, this burner’s igniter still continues to spark after the flame is established. Why?This cook top is on its second spark module. I suspect that the original one wore out because if one waited many minutes the sparking would finally stop. When I replaced it I installed an external switch in its power line so we can turn it off after a flame is established, but this is an inelegant and somewhat inconvenient solution to the problem because the switch is located in a drawer below the burner.Any help in improving my understanding of the system or in making it work as designed will be greatly appreciated.
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