I have a Carrier model 394GAW000100 gas furnace. It is set to light off at 4:30 AM so that the house will be somewhat warm by the time I rise at 5:00 AM. About 3 to 4 times a week the furnace does not light off. An inspection reveals that the pilot ignitor is visibly sparking (accompanied by the usual ticking) but light off the pilot does not occur. A quick click of my barbecue lighter near the ignitor sets off the pilot and normal burner light off occurs. Generally, the furnace operates normally throughout the day, however, occasional failures of the pilot to light off have occurred. What do you think?

Clean the pilot orifice to make sure the pilot is getting a good strong stream of gas so the spark ignitor will light it off. Note: Do not increase the pilot orifice hole size while cleaning.

Also one thing to add to what hvac said is to use a file or a sand cloth and knock the rust off the pilot where the flame comes out. If rust forms the sparker may be sparking to a point on the pilot where the gas in not coming out. Cleaning may cause it to spark every time where it is suppose to.

Thanks for the responses but after performing the cleaning operations, the problem still exists. What do you think about replacing the ignitor, spark ignitor box and the spark electrode? It would seem that these are about the only components that could cause the problem .

Do you have one of these for a pilot?

Yes, it is an LH68005. Mine is mounted at a 90 degree angle from the furnace burners.

Is that the part you took apart and cleaned the orifice in?

Yes although it didn't appear that cleaning could possibly affect the pilot orifice. I couldn't take it apart but I cleaned it quite thoroughly.

The pilot orifice is inside the pilot assembly. It will usually fall out if the brass nut and aluminum tube is removed from the assembly. It is important to make sure the pilot hole is unrestricted.

For some reason the spark from the ignitor is not in the stream of gas coming from the pilot.

Something you can do to test the power of the spark is to use a piece of metal like the tine of a fork put it in the stream where the gas comes out, now turn on the furnace and watch the spark, if it does not spark to the fork then move it around until it does, when you get the fork in a place where the spark hits it but it does not light then move the fork a bit until it does light.
This will tell you that the spark is good enough. It also tells you that the spaark is not hitting the right place on the pilot metal to ingite the gas. You might even try bending the little hood on top of the pilot to make the gas flare out more.

I really don't think you need to replace a bunch of parts. I do hole you get it worked out.

Man this is crazy. The past three nights the outside air temperature was around 40F and the furnace lit off each morning. Every morning that the temp was at or near 32F I had to use my barbecue lighter to get it going. Can cold soaking cause this problem??

Tap the three wire pilot next time it has a failure.

Quote:

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Originally Posted by letmetellu

For some reason the spark from the ignitor is not in the stream of gas coming from the pilot.

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This bears repeating. Next time the problem surfaces, try viewing with a small mirror and as little light as possible. Look for spark "leakage" where the wire connects to the electrode.

Quote:

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Originally Posted by hvac1000

Tap the three wire pilot next time it has a failure.

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This is what I've been doing for the past week or so when I get only sound, but it doesn't fire. What's the fix?

Replace the three wire pilot.

I have a 9 year old Carrir heater model # 'PT7460-C210AP' and the pilot light does not fire off.
Is there a sensor or some other reason the Pilot will not spark that I should look at prior to replacing the pilot light?