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Bryant Gas Furnace - ignites, goes out, ignites, goes out -- 3 wire pilot burner

Bryant Gas Furnace - ignites, goes out, ignites, goes out -- 3 wire pilot burner


  #1  
Old 10-10-11, 10:32 PM
J
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Bryant Gas Furnace - ignites, goes out, ignites, goes out -- 3 wire pilot burner

Hi. Thanks for offering your help as I struggle with my furnace. I did a lot of online research (including this forum), read some conflicting advice, and now am trying to figure out what makes sense.

Furnace: Bryant Gas - model 395 BAW 036095
[this seems to be made by carrier ... but this old model
does not have a manual listed in either of their websites]

Symptoms:
Furnace ignites .. but once the main gas jets are burning, they go out almost immediately. The igniter kicks in again and lights, and main burners come on .. and then go out again. This process repeats over and over and over. It generates some heat, but it's clearly not right, and I figure the igniter is going to get worn out in no time if this continues.

Research:
I see lots of advice about cleaning flame sensors, but cannot find such a sensor on my unit. It seems likely that I have a "Carrier 3 wire pilot burner assembly," which has some kind of built-in heat switch. Please see these photos, which should make it clear (assuming that you can recognize such things).





One website had this comment:
"The 3 wire pilot is serviceable to some extent. Pull the orifice and clean inside pilot body, also make sure orifice is not restricted. Orifice may be cleared NOT resized. Typically not enough flame impinges on bi-metal strip. The switch portion is not field serviceable."

Questions:
1) Am I likely to make any headway on this problem just by removing and trying to clean this assembly ?
2) If it is worth trying to clean this, how do I release the bracket ? (please see photo ). It looks like there are a few different screws, and I'd rather not undo something that messes everything up !
3) If cleaning does not fix the problem, is this assembly something that I can replace myself, or is that a bad idea ? (I'm cautious and meticulous, but certainly not competent at plumbing, and don't want to mess with anything dangerous !).
4) Is there something else I can try, or should I just bite the bullet and bring in a professional (which will probably cost more $$$ than I earn in a week ...).

Thank you for any light you can shed on this !

Jon
 
  #2  
Old 10-10-11, 11:07 PM
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Yes, the pilot burner and pilot orifice need to be cleaned.

Remove the screws that hold the bracket in place, then bend the length of the pilot tubing to pull the pilot burner out.

Get access to the pilot burner by using a 3/16" open end wrench to loosen the brass ferrule that holds the pilot tubing into the pilot burner.

Clean the pilot orifice with a wire from a wire brush.
 
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Old 10-11-11, 02:50 PM
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Seattle meant 7/16" open end wrench..... Often, very often the bimetal wears out in those old 3 wire pilot assemblies. If you call a pro I would have a new 3 wire pilot sitting there waiting on them so when they tell you that you need a new one you can say I'm not paying that price, but how much will it cost if you put my spare 3 wire pilot assembly on for me.
 
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Old 10-11-11, 03:16 PM
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Oh, yeah. 7/16.

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Old 10-11-11, 05:00 PM
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dumb luck ?

Hi guys -- thanks for your encouragement.

If you don't want the long story, the answer at the end is that the furnace now seems to be working fine -- but I really don't know why .... Here's what I did:

I tied myself into a pretzel shape and managed to use my socket wrench to release the hex head bracket screws. I gently bent the tube to give me a limited sort of access to the business end of the pilot assembly.

But then I got no further. In the cramped space, trying to hold the bracket with one hand and turn the nut with the other (yes 7/16 was correct) -- just could not get the leverage to loosen the nut.

Couldn't really see anything, couldn't really access anything ... so I gently wire-brushed the exposed wire end [the igniter ?], and then took a bent piece of floral wire and poked it around randomly inside the end of the pipe.

I felt pretty frustrated, like nothing had been accomplished, and laboriously re-aligned the bracket and secured it in place (this work is tough on the knuckles). Opened the valve to the gas, threw the switch to allow power to the unit ... then went upstairs to engage the thermostat for heat.

And ... it just worked ! Lit the burners, stayed lit. I let it run about a half hour, then shut down (no need for heat tonight).

Thanks again for your advice and encouragement. I have no confidence that I really did anything of consequence, but I'm not too proud to accept a lucky break if it comes my way.

Let's hope I'm not back in a few days saying that the fix didn't last ...
 
  #6  
Old 10-11-11, 05:39 PM
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Sometimes the nut is on there pretty good, just as you describe.

When that happens, gently hold the body of the pilot burner with a pair of channel lock pliers while you loosen the nut with the wrench.

I've always gotten that loose with that method.

Cleaning the pilot burner is a maintenance task that should be done each year to insure reliable operation of the furnace. Also, you need to remove and brush rust and debris from the furnace burners while you have the pilot burner removed.

I use a long 1/4" magnetic nutdriver to remove and reinstall the screws that hold the bracket in place.

Doing this is about a ten minute job. For me.

I know such things are a lot more of a challenge for DIYers --- you did fine. You did what you could with the methods suggested to you.

You did what cleaning you could, and apparently that's good enough for the time being. But the problem will likely recur, and when it does you will have the additional methods described above to help you along.

Do check the burners. If the burner ports are getting plugged with rust and debris they need to be removed and cleaned or you will get the heat exchanger plugged with soot and the furnace making a lot of carbon monoxide.
 
 

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