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Old 01-26-2010, 06:16 AM   #1
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Cobra Furnace - Trouble staying lit!


The furnace locksout after 3 tries. After turning off the power circuit switch
on the furnace, and then turning off the thermostat switch; and then turning them on again in reverse order the furnace will ignite and stay lit until temperature.

If the furnace is turned off before the end of the 4 tries has complete the lockout - it will not start at all until the cycle completes. I have put in a new control board this fall. It appears the code is either 13 or 14. Both have to do with ignition. The igniter seems to work just fine in the cycle.

I have put in a new same type filter that has worked successfully, in the furnace, in the past. I have cleaned the flame sensor and I am wondering if the next step is to check the flame roll-out switch or other component.

Where do I find the schematics for this Cobra model furnace so I can locate the various components? I do have the electrical scehmatics.

Would appreciate any other advice that can help me since it is tough during the economic period to pay for repairs by outside company?

Thanks is advance. I going to work now and will be home later to see replies.

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Old 01-26-2010, 06:39 AM   #2
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Cobra Furnace - Trouble staying lit!


Did you clean the burners yet? Hit the face of them with some fine sandpaper.

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Old 01-26-2010, 06:57 AM   #3
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Cobra Furnace - Trouble staying lit!


How did you clean flames sensor? Is the flame sensor had black marks on it still? Roll switch will pop and you have to reset it your self so I think roll switch is fine.
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Old 01-26-2010, 11:45 AM   #4
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Cobra Furnace - Trouble staying lit!


Check the ground. If it doesn't have a good earth groud you will have problems.
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Old 01-27-2010, 06:02 AM   #5
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Cobra Furnace - Trouble staying lit!


I checked the two ground wires just inside the front inspection panel. One was tight and the other was loose. I tighten the one that was loose, but the problem still persists.

There is a component that goes into the furnace just inside the inspection panel, that I think is the flame detector, which is about 3 inches long and has a flat tip at the end, it appeared to look in pristine condition. I took fine sand paper to the bottom of it anyway and the problem persists. I sure would like to see a schematic of the
furnace components. Does anyone know where I can see one on-line?

I will clean the burners when I get home from work tonight. Now the furnace takes more flame out recycles to start. Very odd!
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Old 01-27-2010, 06:13 AM   #6
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Cobra Furnace - Trouble staying lit!


Looks like you need to get out volt meter
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Old 01-28-2010, 05:19 AM   #7
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Cobra Furnace - Trouble staying lit!


I found the flame detector. I cleaned it with fine sandpaper. It was fairly corroded. Then I found the the tiny reset switch for the Down Safeguard Switch and the Flame Rollout Switch and pushed those tiny reset buttons.

Only the blower comes on now and will not go through a flame cycle like it did before. I wonder if pushing those reset buttons caused a fault in those switches. Before these actions, the furnace would go through several restart cycles and eventually stay lit. How do you use a a meter to check if the switch is good or bad? Looking for answers?
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Old 01-28-2010, 05:24 AM   #8
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Cobra Furnace - Trouble staying lit!


I am thinking that the Flame Rollout Switch is defective. What say you?
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Old 01-28-2010, 05:29 AM   #9
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Cobra Furnace - Trouble staying lit!


How do I use a volt meter to check if the switch is okay?
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Old 01-28-2010, 06:13 AM   #10
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Cobra Furnace - Trouble staying lit!


With the thermostat calling for heat your meter should show 24 volts from one side of the roll out switch to ground and zero volts when checked from terminal to terminal.
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Old 01-28-2010, 01:12 PM   #11
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Cobra Furnace - Trouble staying lit!


By accident, I left the flame sensor disconnected after reinstalling it and the furnance went through it's 4 phase restart again. So I reconnected the flame sensor and wa-la it stayed lit. I believe the flame sensor is bad.

Question: When you check the flame rollout swith with the volt meter, do you have the power on to the unit and put one red lead (+) to switch terminal and the Black (-) lead to the ground and do the same to the other terminal as well? I checked the continuity from one terminal to the other on the rol out switch and it completed the circuit. I did the same with the down draft switch and it had continuity as well. Is this the proper way to check it?

Thanks for your help!
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Old 01-28-2010, 03:41 PM   #12
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Cobra Furnace - Trouble staying lit!


Its good to clean that every year but you need to have hte furnace service once awhile from a pro to ensure it saftey.
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Old 01-28-2010, 05:12 PM   #13
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Cobra Furnace - Trouble staying lit!


Quote:
Originally Posted by Ican View Post
By accident, I left the flame sensor disconnected after reinstalling it and the furnance went through it's 4 phase restart again. So I reconnected the flame sensor and wa-la it stayed lit. I believe the flame sensor is bad.

Question: When you check the flame rollout swith with the volt meter, do you have the power on to the unit and put one red lead (+) to switch terminal and the Black (-) lead to the ground and do the same to the other terminal as well? I checked the continuity from one terminal to the other on the rol out switch and it completed the circuit. I did the same with the down draft switch and it had continuity as well. Is this the proper way to check it?

Thanks for your help!
Lots of ways to check limits/ roll out switches. Continuity with the wires removed is perfectly fine. Terminal to ground just lets you know there's voltage getting that far. Terminal to terminal shows if it's open or closed without removing wires. It all works out the same but for a service tech checking componets while energized is a lot faster. Can check between the beginning point and and the end point and eliminate the whole series of componets as a cause of trouble in one move.
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Old 01-29-2010, 02:03 PM   #14
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Cobra Furnace - Trouble staying lit!


It was the flame sensor. I finally got it to work after much cleaning.

Thank you very much for all your help.

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