Gas and Oil Home Heating Furnaces - furnace is recycling too often

I have a four year old kenmore nat gas furnace and it is shuting off every minute or so and reigniting itself. It has been doing this for a about a month now. What do I need to check? I thought it might be the pilot orifice but I'm not sure. I had heard that a dirty orifice can cause the gas to shut off. thanks

Does the house blower stay running after the burners stop firing? If so, you may have a limit switch that is tripping on overtemperature. Either a defective limit or insufficient air blowing through the furnace's heat exvhanger.

When was the last time you replaced the filter?
Have you perhaps installed a new filter that is significantly more efficient (and hence restrictive)?

What is the purpose of the limit switch?

Is a smart switch that senses the temperature of the air as it goes through the furnace's heat exchanger. The air should get hot, but not abnormally hot...if that was to happen, the otherwise normally closed contacts of the limit switch would open, interrupting the flow of electricity to the gas valve, which will then close, shutting off the burners, until temperatures drop. After a normal temperature is reached again, the switch contacts would automatically close back again.

http://www.freeimagehosting.net/uploads/77bc1855d8.jpg (http://www.freeimagehosting.net/)

The furnace blower does continue to run until reaches the pre set temperature then shuts off. I have an air bear filter system and it was installed when the furnace was installed. I replace the filter about once a year. thanks

Once a year is too many months in between filter changes. If I'm not mistaken, this is a pleated filter. replacement intervals of 3 months are more adequate.

At any rate, try this: remove the filter, close-back the filter rack access door and let the furnace run without the filter (just for the purpose of this test).
Let that furnace run for a good 5-to-10 minutes. If the burners do not shut-off with the filter removed, the filter is your problem.

I changed the filter because it looked dirty and I took apart the igniter to see if the orifice was pluged and I could see light through it. So, I put it back together and she ran for about three minutes before shuting off and then starting again. It did this two or three time real close together and it ran for a minute or so before shuting off and restart again. The pilot light looked longer than it should. I'm really considing replacing the limit switch now. Unless,I need to check something else. thanks

Might turn the power off to the unit. Then put a jumper across the limit switch control . Turn the power back on and see it the furnace will stay on then. This should tell you if its the limit.

Run the test I recommended on posting #6, it will tell you if the filter is causing the limit to trip.

I put a jumper across the terminals of the limit switch and it ran for about two to three minutes before shuting down and then reigniting. Was I suppost to jump across the terminals or the wires? Because I jumped across the terminals. I did not know it that makes a difference or not. What is the next thing I can check out with the furnace? thanks

I ran the test in post #6 and same thing, it runs for two or three min and then starts cutting out and restarting every thirty sec or so. Another thing, I've fail to mention is that the igniter or sensor switch is making a real loud noise when it ignites the pilot. thanks

Spark ignition to pilot? Have you tried to remove the whole pilot assembly out of the furnace to make sure that any flame sensor and al the connections of the metal is clean so current can correctly get back to ground or to the board. Intermittant pilot systems can have problems with insufficient gas through the orifice down at the end of the pilot assembly, or a problem with it's flame sensing capability.

Kenmore is not good at making their tech manuals available online, so, some pics will be helpful here. Also, pls provide the MFR & M/N of the thermostat you have at home.

My thermostat is a Honeywell and I think the s/n is 6000-48951. The is an Enery Optmizer thermostat. It was installed last july by the power & light company,locally. It is suppost to turn off the a/c during peak times in the cooling season while the fan continues to run. I'm not going to have any pictures til my batteries charge up for the camera,which will be later in the day. thanks

When I got home this afternoon, I turned the furnace on and went downstairs to see if it would cut out. It ran for twelve min before it cut out and that is because it had reach the temp I set. The only thing I did to the furnace was change the filter. It seems as thought the dirty filter was caused the problem. Will someone tell why that was so, because I'm clueless. I know a dirty filter will restrict the air. But these air bear filters are five inches thick and I thought because of their size that they did not have to changed but once a year. Do the new furnaces have a sensor that makes it cut out when there is not enough air? thanks

Good to read that things are working out for you. The filter was suspect from the very beginning.
I think you're using too restrictive a filter for the speed selected in your furnace.

And pleated filters, which is what you have there, should be replaced every 3 months or less, at most, not once a year.
They may look clean, but dirt piles up in between the fibers, so they "look" but are "not" clean. And the longer you wait, the more restrictive they become.

A dirty filter slows down the air flow, so the heat exchanger starts overheating (no air, no heat removal from there)...which in turn trips the limit.

The sensor that makes a furnace cut-out when there is not enough air IS the limit switch.

But you may also have to look at the thermostat programming here. You say you have a Honeywell, but the M/N instead of the S/N is what really helps here with troubleshooting.