furnance main gas valve

[TimW]

We have a Lennox gas furnance, standing pilot model, about 15 years old, equipped with a White-Rodgers main valve. Last year, I installed a CO/Gas detector, about six feet from the furnance.
On two occasions over the winter, the Gas Detection alarm triggered, and on the second occurance there was a "slight" odor of gas. Therefore, I called for service.
After an extended time, the serviceman claims he finally detected a higher than spec release of gas from the main valve while closed! I was told I should have this valve replaced. Both times the gas alarm triggered, the furnance was running.
That was two weeks ago, and I have been using the furnance, only shutting the gas off while we sleep. It seems to work fine, no alarm, and no smell of gas.
Was I dealing with nuisance alarms? Is a small odor of gas sometimes normal? Should I go ahead with the valve replacement?
Too complicate this further, I noticed a tiny blue flame shooting out & down from a compression nut feeding the pilot assembly. While moving the small tube feeding the pilot, I choked off the flame. Obviously, a very small leak exists there, and should be fixed. Could that minor leak have triggered the alarm? The serviceman says not, and still claims the main valve has an intermittant problem.

[Wgoodrich]

I would say your problem is two fold. I suspect your furnace needs a professional cleaning. What happens over the years is soot builds up in the vanes of the heat exchanger above the main burners. Also you need to check for a partially plugged flue. Have your furnace cleaned professionally and clean your flue professionally. This should solve your gas problem being detected. When the gas turns on and the furnace needs cleaned the flames tend to flow outside the heat exchanger out into your work area outside the affects of the flue draft. This will cause your CO detector to react. What is often happening the vanes get plugged with soot, the flames open on full and the flames and exhaust does not have any place to go due to the soot restriction and lack of drafting through your flue. Once it warms up the flue warms up increasing the up draft and sucking the flame back into the heat exchanger.

To know if this is your problem water the main burners and turn on your main burner. If flames like back toward you outside the heat exchanger this is your problem.

The side flame you are seeing on your pilot light is commonly a partially plugged pilot orfice. Gas has residue. As the years go by the orfice of that pilot restricts making you adjust higher gas pressure on your pilot light to maintain normal pilot flame to ignite your main burner. This higher gas pressure on your pilot light eventually will back feed through your air intakes of your pilot light. Take out the pilot assembly and use an orfice cleaner and clean out the small hole the gas passes through. This should solve your side flame problem.

Good Luck

Wg

[bamaman]

Wg is dead on about the cleaning. Most furnaces should at least be inspected if not cleaned every 5 years. Under certain conditions, more often. You didnt state if the furnace was LP OR natural, but, if LP, make SURE there are no leaks. There is also the possibility of a hole in the heat exchanger. Sounds to me like the service man may be leading you wrong on the gas valve. There are NO acceptable limitsof gas leakage by a valve with the unit off !

Be careful about the possibility of holes in heat exchangers. This is why CO detectors are installed, to detect this possibility. At the least a hole in the exchanger can cause you and your family to be sick. At the most, IT CAN CAUSE DEATH. Be on the safe side. I suggest you call your local gas company. They are generally straight up and can provide you with a quality service company referrence.