Hot surface ignitor function & safety Q

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Old 01-10-11, 09:21 AM
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Hot surface ignitor function & safety Q

OK I assume (forgive me) that the ignitor in my oven somehow performs the dual function of igniting the gas AND acts as a thermocouple to "tell" the gas valve it's OK to open. But how does it do both at once? My ignitor glows but the oven won't light. This is after a few weeks of it taking a long time to light, and me smelling gas. Now the gas valve won't open at all so the ignitor must not be getting hot enough??

But again--how does it do both functions at the same time with only 2 wires?

Just trying to understand while I wait for my replacement ignitor to ship.
 
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Old 01-10-11, 09:41 AM
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There should be a seperate flame sensor. If the igniter glows and the burner does not light then it sounds like the gas valve is not opening. Sound like a control board issue.

Igniter with flame sensor.



What is the make and model of your oven?

Mike NJ
 
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Old 01-10-11, 06:52 PM
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New igniter arrived. Glows noticeably brighter & now gas comes on & lights immediately. Before removing it I measured the current draw and compared. 2.5A on the old and 3.5 on the new. I've read they can just get dim with age. My range is over 15 years old.

I found a good description of how the current through the igniter is in series with the gas valve. When the igniter gets weak the current drops and then there's not enough current flow to operate the gas valve.

I still don't understand what safety there is to shut off the gas if the burner goes out. No sensor visible and the only wires are the 2 igniter wires.
 
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Old 01-11-11, 04:38 AM
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Hello: guy48065

I still don't understand what safety there is to shut off the gas if the burner goes out. No sensor visible and the only wires are the 2 igniter wires.
EXCELLENT Question! Has been asked several times before but worth repeating again for those whom are new to the forum. (Pertains to an HSI glow igniter.)

Answer is: As long as the HSI remains on (hot and glowing) the current value remains constant, gas valve remains open. When oven temp is reached, electrical power to HSI is cut off, the gas valve closes. That's how the safety system works. Either allows or denies gas to flow.

Also why an HSI may seem to be glowing but not hot enough to ignite gas. HSI has to be hot enough to ignite gas. Which is determined by electrical resistance.
 
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Old 01-11-11, 03:21 PM
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Ah--so the HSI stays on as long as the gas is flowing? I thought it turned off once lit. In my oven it's hidden under a panel and I've never thought to watch it when it was working fine
That does explain why there's no flame safety included on this type system.

I'm now even more impressed that mine lasted 17 years considering how much time it's glowing.
 
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Old 01-11-11, 07:43 PM
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You kind of answered your own question when you said the old igniter was showing 2.5 amps. Your is a "Norton" and the minimum amps required to open the valve is 3.2. The range is 3.2-3.6 Bravo for taking reads, that is nice to see. Now the reason you smelled gas, the amps required were to low to fully open valve or enough for there to be ignition, so a small amount of gas was passing with no ignition. So as you can see, the igniter has a dual function. If you wanted to look at the gas valve you will see a label with a picture of the igniter and also the values in amps as well as volts .
 
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