Question On The Ever Popular Pilot Light - HVAC - DIY Chatroom Home Improvement Forum

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Old 10-14-2012, 06:48 AM   #1
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Question on the ever popular pilot light

Hi and thanks in advance!
I purchased my home just over a year ago. Built in the early '80s. Furnace is original. Propane fuel. Comfortaire.

I was doing some landscaping this summer and accidentally discovered my propane line. (which was buried a mere 3 inches under the ground)
I didn't break it but merely creased it with a pick axe.
I called the LP company to have it repaired. He did and then he did a pressure/leak test on the system. Of course all pilots in the house had been extinguished when I turned off the gas valve and he discovered a slow leak in the system. We traced it back to the furnace. When I shut off the gas line to the furnace the leak disappeared. He told me it was a faulty thermocouple.
I didn't worry too much about it as this is a minor repair so I let it go until now.
Yesterday I purchased a universal thermocouple and replaced it.
It lights fine and the furnace functions correctly.
My question is when I blow out the pilot light the gas continues to run still. I can stick the lighter back in there after I blow it out and it will relight without pushing in the pilot button.
How long does it take for the thermocouple to cool and close the pilot valve?
I waited as much as 15-20 seconds and the gas continued to flow.
The pilot light is quite strong and hit the thermocouple directly. It is getting lots of heat and should be generating plenty of MV.

I also discovered that the pilot line has a leak right where the flare nut connects the line to the pilot burner. There is a secondary small flame coming from the seam along with the standard pilot light. I may have to replace the pilot line as well.
The sheet taped to the side of the furnace said it was inspected and cleaned shortly before I bought the house.
Any thoughts?


Last edited by Bushman; 10-14-2012 at 06:50 AM. Reason: spelling
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Old 10-14-2012, 07:57 AM   #2
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Yikes! You have a couple of serious problems. Not a pro here but it sounds like your gas valve pilot is stuck open. It should respond to the t-couple pretty quickly to shut off flow if the flame goes out. The other leak not good either. If it was me I'd get a pro in there ASAP to repair.... or at that age maybe even consider replacement depending on repair (probably needs a new gas valve) and operating costs. Not completely sure but those problems might warrant the unit be red tagged with the gas turned off until fixed. The pros will weigh in soon and give you a more definitive answer.


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Old 10-14-2012, 09:52 AM   #3
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Early 80's? At least 20 years old or more now?

My inlaws was of the same vintage....they just replaced it unit is more effecient and quieter...might be a good option.

The new stuff uses electronic ignition.
Even if you are on the right track, you will still get run over if you just sit there.

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Old 10-14-2012, 11:28 AM   #4
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main gas should drop out seconds after the pilot is blown off the TC .... the flame heat generates the MV replace the valve it is sticking....shut the main gas into the furnace and swing the TC out so you can use a BIC lighter to simulate the pilot call for heat toggle up furnace flame on flame off TC valve should click off...might be shutting off but no enough crap in the seat within...don't mickey mouse with the valve replace it...another service tip is... finger tight will make main valve/pilot stay lit.... just unscrew the TC where it goes into the valve...result pilot off/shut down main burner before it is removed..that trick is a typical residential test for a seasonal heating start up

Last edited by biggles; 10-14-2012 at 11:33 AM.
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Old 10-14-2012, 12:39 PM   #5
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A 15 to 2o second test is too short a wait to tell you anything!

*Turn off anything in the furnace area that makes any noice.
*Blow out the pilot.(that includes any ignited gas seep that maybe burning below the pilot)
*Time in seconds how long the gas valve takes to lock out. A click or a clunk from the gas valve will tell you it's shut off. If you keep a hand on the gas valve after blowing out the pilot, you can also feel that click or clunk when the pilot solinoid shuts off.
*If it does not click off within 75 seconds after the pilot is blown out, turn off the gas.
If it does shut off, it will usually do so within 30 and 60 seconds.
There are numerous facters in why a lock out takes the time it takes but under 75 seconds is an allowable delay for a standing pilot system. Any more and you should change that valve.

The leaking pilot tube gas will need to be addressed (tightening a loose ferrule nut/ redoing the pilot tube end or replacing the whole line & ends.

Last edited by how; 10-14-2012 at 12:43 PM.
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Old 10-14-2012, 01:35 PM   #6
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agree with how...if the thermocupler is good it may take 1 min to 1min and 1/2 before it trips pilot the test again ....ben sr...


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