Furnace Burners Ignite Then Shut Off

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Old 10-19-19, 12:08 PM
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Furnace Burners Ignite Then Shut Off

I have a Weather King furnace, and it is not working properly. When I turn it on, I hear the system starting. It takes approximately 15-20 seconds for the burners to ignite. They stay on for about 5-6 seconds and then shut off. The system will repeat this again 2 more times, and the same thing happens. Is there anything that I can do to troubleshoot this? I can post pictures if that would help. I donít have much HVAC experience, but I have done a lot of electrical. Iím not sure if that helps at all.
 
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Old 10-19-19, 12:58 PM
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check for an error code.

likely just a dirty flame sensor.
 
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Old 10-19-19, 02:55 PM
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Is this error code displayed by the green led on the control board? It blinks 2 times, then goes out, blinks 2 times, etc.
 
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Old 10-19-19, 03:25 PM
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the error codes should be listed on the schematic - open the blower compartment access panel and check the side that normally faces in.
 
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Old 10-19-19, 04:47 PM
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I checked the schematic, and it says 2 blinks is ďPressure Switch Open.Ē I donít know if this matters, but my blower went in July. It was replaced with a new one. The AC worked fine after that. I donít know if that would have anything to do with this.
 
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Old 10-19-19, 05:35 PM
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No it doesn't.

Monitor voltage drop across the pressure switch during the cycle, see if/when it drops off.

Set your meter to read ac volts - you're looking for 24v ac +/-.

If the switch is dropping out, disconnect the pressure switch hoses and make sure the hose and connections are clear.

If you have a high efficiency furnace vented with plastic pipe, make sure the drain lines and trap are clear.

Check the intake and exhaust outside for blockages.
 
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Old 10-24-19, 02:11 PM
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I hadnít responded, but I was able to get the unit working on Sunday. I didnít do anything complicated. I checked the hoses, disconnected the wires on the pressure switches, and cleaned the terminals. There didnít seem to be any debris anywhere. I also cleaned the flame sensor. It started working and was fine until this morning. Itís doing the same thing again. I got my multimeter and tested both pressure switches. When the unit calls for heat, the voltage goes to 26v and then 0. The burners are on for about 3-5 seconds and then turn off. When the unit turns off, I donít see much of a jump on my multimeter, but it does occasionally say OL. Any advice would be greatly appreciated.
 
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Old 10-24-19, 02:31 PM
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When the unit calls for heat, the voltage goes to 26v and then 0.
That is the normal response of the pressure switch.
It should stay at 0v as long as the inducer blower is running.

You are checking for voltage. The meter should be on an AC scale over 24vAC.
OL typically only appears when you are in ohms mode.

Are you still getting a code for open pressure switch ?
Pull the pressure switch hose off of the inducer and clean the tiny orifice down inside the fitting.
You can use a pin, a broom bristle or small drill bit.

Pressure switch issues can be tough to localize. You may need to call in a service tech on this one.

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Old 10-24-19, 03:27 PM
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Thanks, PJ. I may have to call a tech in on this one. It's over my skill level. What's so odd is that I actually got it working for 4 days. I thought maybe there was an exhaust blockage, but I doubt I would have gotten it to work at all. I'm still getting the pressure switch error, but I'm wondering if it's possible that's it's a bad flame sensor. I disconnected it just to see what would happen, and it seems to be doing the exact same thing.
 
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