Old Bryant Gas Furnace Pilot won't stay lit

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Old 01-31-12, 09:42 AM
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Old Bryant Gas Furnace Pilot won't stay lit

Hi. My mom's old Bryant gas furnace is having the same problem. I found this thread that describes the same problem with the same type of old gas furnace: http://www.doityourself.com/forum/ga...-lit-help.html

We changed the thermocouple and the pilot is still not staying lit. The furnace is the same type and vintage, late 70s to early 80s, as the other thread.

I will light it and it will turn on the main gas burners to heat the rooms but after the main burners turns off, the pilot light is also out. The next time the furnace turns on, it is blowing cold air. I have to keep relighting the pilot for the furnace to work properly.

We can not afford to get a new furnace at this time so we need to get this one working.

I do not think the pilot light is all blue but am not sure since the view is partially blocked.

Any help or suggestions will be appreciated. Also, does anyone know how much it might cost to get this furnace serviced? She's on a limited income and any work I can do myself will help her tremendously.

Thanks,
Frank
 
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Old 01-31-12, 09:47 AM
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The most common problem is a pilot burner that needs to be disassembled and cleaned. Describe thew appearance of the pilot flame in detail. What color(s) are in the pilot flame? Is the flame sharp like a small blowtorch, or a lazy flame more like a candle flame?

Does the pilot flame engulf the last 3/8" of the thermocouple?
 
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Old 01-31-12, 10:34 AM
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The flame does not look like a blowtorch but more like a lazy flame. As far as it engulfing the thermocouple, I can not see since the pilot and thermocouple are blocked from view behind some sheet metal shielding.

If I need to dissemble and clean this burner, where can I find the steps to do this?
 
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Old 01-31-12, 12:44 PM
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Yes, cleaning the pilot burner and pilot orifice is likely to solve the problem for no cash outlay.

But you have to be willing and able to do the job. And there aren't any detailed directions since there are a wide variety of different pilot burners.

In general, you need to shut off the gas to the pilot burner. Use a screwdriver or 1/4" nutdriver to remove the screws holding the pilot burner to the furnace sheet metal.

In most cases, you can gently bend the pilot tubing to move the pilot burner out where you can work on it.

Use a 7/16" open end wrench to loosen the brass compression fitting that holds the pilot tubing to the pilot burner. The pilot orifice is held in place by the bezzle at the end of the pilot tubing. The pilot orifice needs to be removed and cleaned or blown out with compressed air.

Some pilot orifices can be cleaned withe a wire from a wire brush. Some have holes too small for this and you can try compressed air or blowing through it to clean it.

Use a wire brush to clean debris from the rest of the pilot burner.

Reassemble the pilot burner. Light the pilot burner while it's outside the furnace and check it for a good burner flame and for the flame engulfing the thermocouple. It should hold the magnet and the pilot should stay lit.

Use a soapy solution from some water and quite a lot of dish washing detergent to make a soapy solution to check for leaks on the compression fitting. Reinstall the pilot burner in the furnace and check for leaks on the pilot tuning at the gas valve.
 
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Old 01-31-12, 02:18 PM
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Thanks for the info. I'll try this and see if this solves the issue. I'll let you know!
 
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Old 01-31-12, 02:27 PM
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When a pilot wont stay lit, the reason is a dirty pilot about 90% of the time.

A bad thermocouple about 5% of the time.

A bad gas valve about 1% of the time.

Miscellaneous other problems 4% or so.
 
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Old 01-31-12, 06:20 PM
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Ok so I had a profession HVAC guy come and take a look at it before I tried to clean the pilot just to see what he thinks might be the problem.

He removed the sheet metal cover that was covering the pilot light from view. At this point, the pilot light was already off. With his flashlight, he pointed out some rust and residue inside the gas chamber (i dont recall what he called it but its the part where the burners are housed). With this, he states that the problem is this which causes the pilot safety switch to turn off. He states I will need a new furnace.

I know I'll need to replace this furnace but with this quick 5 minute inspection, does anyone think he is right, that this rust caused by the burners is the cause? He didn't even try to light the pilot to look at it.

I'm still a little unsure about his diagnosis as being correct. When asked how much it would cost to replace the furnace, he quoted a price for the furnace and another 1k for permits and such.
 
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Old 01-31-12, 07:05 PM
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The burners are in the heat exchanger. It's not unusual to have some rust on the walls of the heat exchanger, especially in an old furnace.

A crack or hole in the heat exchanger is a problem that should result in the furnace being shut off until repaired or replaced.

Rust or scale that is significant enough might require that the heat exchanger be cleaned with brushes that can knock off the scale.

It would be quite common that the burners would need to be cleaned of rust and crud.

Indeed, for an old furnace that hasn't been maintained, inspecting the heat exchanger, cleaning the burners and pilot burner to be sure that the furnace is safe and reliable to operate would be the mark of a good repairman. Doing that along with brushing off moderate amounts of rust from the heat exchanger walls should take about an hour of labor on an old furnace (which is easier to service than most new furnaces).

I'm unimpressed with "repairmen" who are called in and charge people to sell them a new furnace it sounds like they don't need, at least based on what you reported. You DO have an old furnace. But if it can be operated safely you are entitled to do so.

In most cases, a repairman should be able to show an interested homeowner a crack or hole in a heat exchanger in an old furnace. In this case, there doesn't appear to be a claim that there was a crack or hole, and if that's the case the needed maintenance work should be done and the furnace put back in service.

On rare occasions I did encounter furnaces so old and deteriorated that I didn't want to be involved in putting them back in service. Just not worth putting my expertise on the line. Other people might be pickier about such things than I was.

You might want to post some pictures of your furnace.
 
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