Ignition keeps clicking after pilot is lit

[DieselLover]

I have a natural gas forced air furnace (Replaced in 1988 I believe) that has a pilot ignition system (Pilot only turns on when it is needed).

My problem is that the system doesn't fully know that it is lit. The system will come on, the pilot will ignite (within 3 or 4 clicks every time), but the ignitor keeps clicking. Initially, the clicking is very regular (for 8-15 seconds), then it stops for a second or 2, clicks a few more times, waits a little, clicks more times, may wait a little longer, at any rate, it is not allowing the main burner to come on.

After reading a few forums, the ignition sensor was thought to be to blame, so I replaced it Saturday. I also read that a bad ground could cause the issue, so I used a wire wheel on my dremmel and polished up most of the metal on metal contact points anywhere around the pilot. The spark is good and strong (Looks to be white-ish/blue-ish).

What could cause this? It seems to me that the flame sensor may not be getting enough flame. Can that be my problem? The gas regulator that feeds the pilot does not have an adjustment screw, so I cannot increase the flame size that way. Should I replace the pilot jet? Could it just be too choked from time and corrosion? It has a 18 stamped on it and appears to be part of the supply tube. Does it come apart? Or can the supply tube be bought as a whole?

Any insight is appreciated!

[HayZee518]

A gas furnace ignition uses either a flame rod or a millivolt generator to detect the presence of an ignition flame. when it is called upon to light, a high voltage spark is generated across a set of contacts and the pilot valve is opened. If a pilot is not lit during a certain time delay, the burner relay locks out. There may be other timers involved in the circuit for purging the burner chamber. When the sensor detects the continuous flame, the main valve will open.

[DieselLover]

My pilot will light nearly immediately & stay lit while the ignitor will keep clicking (Although it gets intermittent after a while) until I shut off the "heat" switch at the thermostat. The flame rod (Like I said) is new. How close should the pilot flame be to the flame rod?

I'm also questioning the little orifice that regulates the gas flow directly before the pilot flame itself (Like the hole at the base of the flame of a hand-held cigarette lighter). Can those get gunked up or corroded over time? Enough to slightly lessen the flame and not allow enough heat to hit the flame rod?

[HayZee518]

The pilot flame orifice is a set opening. if it's replaceable I don't know. I do know that since early times there's less and less "gunk" travelling along with the natural gas. Early gas lines needed a drip leg for sediment just before the valve. Haven't seen much about drip legs in the last 20 years or so. The intermittent ignition should stay sparking just to establish the flame - then it shuts off after a delay time period. Those parameters are determined by the ignitor manufacturer. I had to replace a white rodgers control on a commercial gas dryer and that had a 90 second purge, with a 15 second spark time. Lockout was 12 seconds after no flame.

[DieselLover]

Figuring that the orifice was the issue and that I was not getting enough flame, I stopped off at the local heating and cooling store. They had exactly the orifice that I needed. The guy told me that there are basically 2 sizes. 1 for LP and 1 for natural gas. I needed the natural gas version (Size 18).

The old one came right off of the end of the pilot feeder tube (Friction fit) and I put on the new one (slid right on). I cleaned up (polished) the area a little more with my dremmel (and wire wheel), re-installed it and it fired right up. My old pilot flame was maybe 3/8" to 1/2" long, now it is 5/8" to 3/4". The ignitor only has to click twice!!! The main burner kicks on after about 5 seconds and everything works awesome now!

So, for a little time and only $12 ($6.50 for the Flame Sensor Rod and $5.50 for the Pilot orifice), my furnace ignites immediately!