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Old 11-12-2012, 01:41 PM   #1
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pilot wont stay lite


ok i have a standing pilot gas valve and the furnace will run a cycle and shut down. then after the blower shuts off i hear a click frm the gas valve and the pilot goes out is my gas valve bad replaced thermocouple still doing it

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Old 11-12-2012, 01:46 PM   #2
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pilot wont stay lite


You'd need a manometer to test (gas) pressure through the gas valve.

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Old 11-12-2012, 01:53 PM   #3
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pilot wont stay lite


were would i get the meter thans

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Old 11-12-2012, 02:02 PM   #4
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pilot wont stay lite


Hvac supply house but not sure they'll sell to the public. Could try Grainger or online.

Digital manometer.

This is what I use, you might find one cheaper.






Have you tried simply thumping the gas valve?
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Old 11-12-2012, 02:04 PM   #5
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pilot wont stay lite


Have you checked the wires to the valve, make sure the connections are solid? A gas valve usually only clicks once as it receives voltage to open. If there were a loose wire then the voltage could be interrupted.
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Old 11-12-2012, 02:11 PM   #6
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pilot wont stay lite


yes try the thump and checked wires.is that meter the one that checks in w.c and no supply houses wont sell to public. thanks
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Old 11-12-2012, 02:17 PM   #7
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pilot wont stay lite


yes, inches in water columns.
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Old 11-12-2012, 02:21 PM   #8
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pilot wont stay lite


ok thank u for ur help
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Old 11-12-2012, 02:32 PM   #9
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You'd need a manometer to test (gas) pressure through the gas valve.

Why does he need a manometer? Pilots will stay lit under the most severe cases of low press.

Standing pilots use a magnetic operator that is held in by the DC millivoltage the thermocouple produces. Either the pilot is partially plugged causing poor pilot impingement or the magnetic operator is weak.

The pilot flame should envelope the top 1/4 of the thermocouple and should be a steady non-wavering blue in color flame.
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Old 11-12-2012, 05:51 PM   #10
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pilot wont stay lite


Sounds like dirty pilot orfice, causing burner to suck pilot flame out when it shuts off.
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Old 11-12-2012, 06:06 PM   #11
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pilot wont stay lite


yep start with addressing the pilot itself...see how strong it is ...make sure it is fully engulfing thermocupler.....ben sr
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Old 11-12-2012, 06:43 PM   #12
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pilot wont stay lite


Watch the pilot flame when the burners shut off. It's not uncommon for a cracked heat exchanger to let air blow the pilot around and cause the safety to kill the gas. And by not uncommon I mean 99 out of 100 times that's the root cause of the problem.
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Old 11-12-2012, 07:08 PM   #13
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pilot wont stay lite


Make sure the pilot flame is enveloping the end of the thermocoupler by either repositioning the thermocouper in the pilot assy sleeve, cleaning or replacing the pilot orifice or by adjusting the pilot gas pressure. Also make sure there are no flames occuring at the bottom of the pilot assy which can heat the cold junction of the pilot.

Watch the pilot flames position to see if the pilot flame moves away from enveloping the thermocoupler during any part of the entire heating cycle.

Let us know what happens.

You can use any thermocoupler adapter in between the valve and the thermocoupler which allows you to use a standard meter to measure the dcmv strength of the thermocoupler and the dcmv pilot electromagnet threashold drop out point of the gas valve.

The only loose wires that would normally knock out a pilot light would be if you had a powerpile system. The coupler needs only to be finger tightened plus a 1/4 turn by wrench.

Last edited by how; 11-12-2012 at 07:15 PM.
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Old 11-12-2012, 07:50 PM   #14
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Originally Posted by Marty S. View Post
Watch the pilot flame when the burners shut off. It's not uncommon for a cracked heat exchanger to let air blow the pilot around and cause the safety to kill the gas. And by not uncommon I mean 99 out of 100 times that's the root cause of the problem.
That number is pretty high. That's like saying 99% of all standing pilot furnaces had ht ex cracks from the factory.
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Old 11-12-2012, 08:03 PM   #15
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pilot wont stay lite


In my career it's been closer to one percent but most of my clients are regulars so annual exchanger checks seldom let a crack advance far enough to effect the pilot.

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