New Bosch HGI8056UC Cooktop sparking continuously

[Albionite]

Brand-new Bosch range with 5-burner cooktop. Converted to LP by service technician. When tested, all five burners spark continuously even if all are aflame. Tested the switches with voltmeter; each is open circuit in OFF position and closed throughout the ON range. Replaced spark module on advice of tech; no change. Checked wiring and the runs to the module correspond to the wires going to the igniters. It's brand-new so no moisture or anything else in the burners or switches, no corrosion. 

The burners do not all behave exactly the same though. The big center burner (which has a different type of switch, a MQS-210H micro switch) sparks continuously throughout the whole range from High to Low, it never stops. Each of the others (with rotary switches) will actually stop sparking in the High part of the range, but all spark from about Medium to Low. They also don't behave the same way if all are on or only one; if I turn on a single burner and adjust it until there is no sparking, then turn on another burner, both will spark continuously.

The flames appear to be correct and there is definitely flame at each of the igniters. Sparks are blue and rapid.

I'm kind of at my wits end here - this doesn't seem to match up with any of the diagnostics I've been able to find for this problem. I've had it apart three times now. Any suggestions?

[ECtoFix]

Just a few things off the top of my head:

• Make sure all burner caps are properly installed so that each burner's flame properly impinges onto the ignitor's tips.
• Since you're familiar with how to replace the ignition module, check the wire going to the EARTH terminal.  Check for a clean and tight connection.  This includes wherever that wire terminates to the range chassis.  The flame sensing circuit relies heavily on a clean and solid ground connection.

[ECtoFix]

I'll add one more thing....

Assuming yours is a 120v range, I suggest checking the power cord and be sure it's installed in the proper polarity.  If the incoming LINE and NEUTRAL wires are reversed, some electronic controls in your range may not function correctly.

[Albionite]

OK thanks for the tips. It's not at my house yet so I'll have to check it next week. It's definitely not the burner caps, we checked those repeatedly. I didn't think to check the cord polarity though - it was installed by a pro. Grounding is something I was starting to wonder about - seems like that's often the cause of these mysterious electrical problems. And the symptoms do seem to point to the flame sensing.

[ECtoFix]

Your range should have a facotory installed 120v, 15a cord on it.

I also advise checking polarity of the outlet as well.  Hardware stores sell a polarity tester for that purpose, such as this one on Amazon:

polarity tester

 

If you happen to own a multimeter, here's how you test an outlet without having to buy that tester:

 

 

 

[Albionite]

Thought I should let you know how this worked out.

The symptoms were pointing to the flame-sensing circuit, and the hints provided by ECtoFix put me on the right track. I began to suspect it was either a faulty ground connection somewhere in the long train of ignition switches and sparkers, or... possibly an issue with the electrical power source. I had been working on it at the appliance store warehouse, using their heavy-duty but long extension cord. At my wife's instigation we had the range delivered to our house where I could work on it at leisure and with known and testable power input. 

You see where this is going, don't you?

The helpful folks at the store delivered it to my house and I plugged it in directly to a wall outlet, turned on a burner and... it worked perfectly. Everything worked fine.

It was the extension cord! Too much resistance, fooling the flame-sensing circuit.  That's why some burners would work sometimes. The flame-sensing circuit is just reading the tiny drop in resistance caused by the greater conductivity of a flame vs. air, but if the extension cord introduces resistance, it can "look" to the sensor like the flame is out.

Bottom line, I have a perfectly functioning brand-new range that I got for half-price and free delivery. Pretty happy with that.