furnace ignitor comes on, gas valve clicks but no flame


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Old 09-12-14, 09:34 PM
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furnace ignitor comes on, gas valve clicks but no flame

I've been having on again off again with our newer furnace. Before it would shut off after being on for a few minutes, which I tracked down to the flame sensor and cleaned it which solved the problem.

Now what I experience is the inductor blower coming on, then eventually the ignitor starts to glow and come on. Then after a brief moment I hear a click come from the gas valve, then after 10 seconds another click (sounds like valve closing) and the ignitor turns off. This will repeat about 5 times then I'll get alternating green and red lights on the board indicating a failure to start.

I'm assuming this can't be the flame sensor since it never gets to a point where there's a flame to sense, and I don't have a multimeter at the moment to see if its the gas valve. Anybody have any other ideas I could try?
 
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Old 09-12-14, 10:40 PM
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Sounds like a flame sensor issue again. To better assist you, please post the model number of your furnace. The flame sensor needs to be very clean to work properly. Over time deposits build up on the rod preventing the proper micro-amps from reaching the control board to let it know the flame is present. This usually happens in about 2-3 seconds. While there is much controversy on how to clean the rod I find that emery cloth or sand paper works well. Others use steel wool or scotch-brite pads. The main thing is that you get the rod super clean. After it is "sanded" it needs to be wiped off with a clean paper towel or soft rag. The rods really don't fail that often and proper cleaning will normally solve the problem you are experiencing.
 
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Old 09-12-14, 10:44 PM
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If you here it click and don't smell gas then there is a distinct possibility of a gas valve problem.
It's pretty rare though.... gas valves are extremely reliable.

There has to be flame present for it to be a flame sensor rod issue.

Are you running on natural gas or propane ?

In order to confirm that it is the valve you are going to have to verify the voltage.
 
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Old 09-12-14, 10:50 PM
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No furnace Pro, but I don't see how it can be a flame sensor issue if you never get flame (as you said). What color does the igniter glow? Red, orange or almost white? It has to be almost white to light the gas. And is it directly in the gas flow?
 
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Old 09-12-14, 11:04 PM
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That's the problem;no flame present. After the igniter comes on the control board is looking for a flame. Since there is no flame the control board cuts off the gas valve. The flame sensing is done via the phenomenon of flame rectification. This is a flame's ability to rectify an AC signal to a DC signal which can be sensed and thus proving a flame exists and it is safe to transition to main burner or continue running. The flame is a conductor of electricity, albeit a poor one, and the DC signal is mere micro-amps and easily disrupted .
 
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Old 09-12-14, 11:17 PM
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Yup.... you described how the circuit works but if there never is a flame then the flame sensor will shut the gas down but not because it's defective..... by lack of flame.
 
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Old 09-12-14, 11:44 PM
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You are correct, sir! Thanks for clarifying that.
 
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Old 09-13-14, 08:56 AM
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Its running on natural gas and the ignitor lights a very distinct orange glow. I'll have to get the model # in a bit, away from home right noe
 
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Old 09-13-14, 08:59 AM
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It should be bright orange to orange-white in color.
 
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Old 09-13-14, 10:01 AM
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Hopefully it may be as simple as a loose plug on the control board. I suggest you check Plug-2 and Plug-10 to ensure they are fully seated. I have circled in red the two plugs on the attached schematic.
 

Last edited by firedawgsatx; 09-13-14 at 10:17 AM.
 

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