standing pilot keeps going out

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Old 01-25-09, 12:56 PM
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standing pilot keeps going out

Hi,
I have a Hydro Therm HCC7-(487) natural gas, 3 zone furnace system probably installed in mid 80's and I live in north Jersey. Last week the pilot light went out on the furnace for the first time ever since 1996 when we moved here. I lit the pilot and the furnace cycle worked but when the furnace cycle stopped the pilot went out. After surfing the web for answers I thought the problem might be either a dirty orifice or the thermocouple. So I bought a thermocouple just in case and I cleaned the pilot burner and tip of the thermocouple with a wire brush. When I started it back up it worked for the rest of that day but the pilot went out again the next day. So I really cleaned the pilot burner and thermocouple this time and tried it again. Well, I had no problem from last Saturday until last night when the pilot went out again. I'm not sure where to look at this point so I tried adjusting the pilot flame using the adjustment screw on the gas valve body but couldn't seem to change the flame size at all no matter which way I turned the adjustment screw. I tried this in both the Pilot position as well as the On position but no change. The flame is mostly blue but occasionally there is a quick tinge of yellow. At present it might work for one heat cycle but then the pilot goes out again. Any advice at this point?
Thanks in advance.
 
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Old 01-25-09, 01:20 PM
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Did you diassemble the pilot burner so that you could thoroughly clean the pilot orifice? That's usually the key to cleaning a pilot burner properly.

Once that's done, you should have a pilot flame that burns with a sharp flame, like a small blowtorch. A lazy flame that can easily be blown around is also easily blown out, which is why dirty pilotm burners cause pilot outages.


Once you are satisfied you have a good piloit flame, check to see if it fully engulfs the top 1/4" or so of the thermocouple.

I don't recommend adjusting the pilot gas -- but it sounds like that adjustment is fully open. Manufacturers typically don't permit a lot of pilot gas pressure on a pilot burner.

If you've done all that and still getting pilot outages, I suppose replacing the thermocouple will do no harm. It's usually the first thing the DIYer doesm, and only infrequently is the actual problem.

If the problem continues, it could be a worn out magnet on the gas valve, which would require replacing the gas valve. I don't recommend that as a DIY job, and having a repairman double check everything before replacing the valve is worthwhile.
 
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Old 01-25-09, 02:44 PM
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Thanks for the reply. I guess I need to remove one of the burners itself in order to get at the pilot burner assembly. The bracket is part of the burner and I can't even imagine how to get the thermocouple out of the bracket without removing the burner which it is mounted on. The bracket assembly is about 1/4 of the way inside the furnace and there is no way to get my hands in there let alone a wrench. Does this seem correct to you sir?
 
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Old 01-25-09, 05:08 PM
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Usually there are a couple of screws or nuts holding the pilot burner in place. And usually these can be removed with a long screwdriver or nutdriver, which then allows the pilot burner to be removed.

You might need to remove the pilot tubing and thermocouple fitting from the gas valve to do that.

Sometimes you may be able to remove those fitting to the gas valve and lift out the whole burner.

But anything's possible for a furnace designer. Look carefully for an easy way first.
 
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Old 01-25-09, 06:38 PM
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Dear Sir,
Thanks again for your help. Here is an update:
It ran for around 3 hours but then it went out again so I changed the thermocouple. I had to loosen the manifold bolts in order to slide out the burners. The left burner has the bracket welded onto it. After I removed the center and right burners I was able to get a wrench in there to remove the gas line and thermocouple. I checked the pilot orifice again and it looked clear. So after I changed the thermo and re-installed everything it fired up and is running now in its first cycle. The only thing that worries me is that the pilot flame now has a little more yellow in it than before I removed everything. Do you think I messed up the air mixture and anything else? Maybe I should have someone look at it if it fails to stay lit now. What do you think sir? Thanks again for your help.
 
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Old 01-25-09, 07:02 PM
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Most pilot are non aerated, which means that the gas mixes with the air surrounding the burner for combustion. A few are aerated bunson burners that typically have a hole somewhere on the body of the pilot burner which sucks in air to mix with the raw gas --- and often gets plugged with gunk.

I hope you cleaned the pilot orifice. Using a wire from a wire brush often works well. But looking at it is no help, and cleaning it as a matter of routine whether it looks OK or not is the correct procedure.

It sounds like your burner assembly is designed to slide out as a complete unit. There are some of those around, and if properly installed have a union which allows the gas line to be disconnected easily.

Perhaps you will be lucky and the thermocouple will solve the problem.
 
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Old 01-25-09, 07:17 PM
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Sir,
Still waiting for the cycle to end. I'll shoot you an update.
Thanks so much.
 
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Old 01-26-09, 04:22 AM
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Well Sir,
It's Monday morning and we still have heat! YAY! I'm going to keep my fingers crossed. Thanks again for all your help.
 
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Old 01-26-09, 06:55 PM
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24 hours since I changed the thermocouple and we're still going. Actually the flame on the pilot now looks good. There is no more yellow tinge to it. Hopefully this is it! Sir, thank you once again for all your help.
 
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