Furnace burner turns off and on

If you have a switch that can manually turn on the fan, try it to verify the fan works. This is what I think is happening. The normal operation should be thermostat calls for heat, inducer fan comes on, pressure switch closes, igniter glows, main burner ignites and then in 30 or so seconds the fan comes on and stays on until the thermostat is satisfied. Once the thermostat is satisfied the burner shuts off and the fan runs for approx 120 seconds then shuts off. I think the control board that automatically turns your fan on is faulty. On most modern furnaces if the auto fan control fails and the furnace gets to hot and limits, when the limit opens and shuts off the burner it also energizes the fan motor to cool the heat exchanger.

this is normal the clicking sound you hear is the system starting another cycle for your furnace to ignite the burners, then turn on tbe fan blower.

This is possible, however it is possible they are missing something simple. I hope you can follow along.
1) Is this a Sealed Combustion Furnace, meaning you cannot get to the burners even after you remove the Door Panels?

2) If yes, is this furnace vented with pvc/plastic piping?
3) If yes, do both pipes go outside?
4) If yes then try this.

1) Turn the main power off to the furnace
2) Remove the Door Panel to the burner section.
3) Turn Furnace back and turn the thermostat all the way up.
4)Look into the burner compartment and tell me if the igniter glows red. If it does and the goes out with the burners not coming on.

5) If you feel comfortable or know of someone that is.
6) Turn the furnace off, remove the panel that conceals the burner compartment.

7) Turn the furnace on, if the igniter glows red and the burners ignite. Your problem is in the venting system. Most likely the intake pipe if it goes outside. It could be plugged or something is blocking it. If the burners do not ignite the next thing to make sure that is happening is that the Exhaust blower is operating and you can feel air outside where the pipe terminates. If you it is but no very strong, then your problem could be the inducer motor or to small of vent pipe.

If you could, send me some information about how it starts up
1) Main blower may come on and shut off, make sure the blower runs in on position 1st then back to Auto position. If it does not, you have another problem.

2) The Exhaust blower should come on next
3) About 17secs. later the igniter should glow red.
4) You will here the gas valve make a click
5) The Burners will ignite
6) The flame sensor rod on the far left hand side of the burner will keep the burner lit. If it is dirty the burners will shutdown.
7)About 90secs. later the main blower will come on.

Turn off power to furnace and remove upper panel only. Turn the power back on and turn the thermostat all the way up. Go back down to furnace and watch the burner section.

This is what you should look for
1)On the left hand side of the furnace near the burner, the igniter should glow red, if it glows red and shuts off without igniting the burner then you have a problem with the venting or faulty pressure switch.

2) If it does not glow red but you have power to the furnace, the ignitier is most likely cracked.

Sounds like either the flame sensor is not working.
The sequence for starting the furnace is:
1. extraction fan on
2. pressure sensor (for fan)
3. ignitor (spark or glow plug) comes on
4. gas valve opens up
5. ignition of flame
6. flame sensor (or temperature sensor)
7. plenum temp. sensor
8. main fan starts
It is most likely that the flame sensor is dirty or gone,
or (and I hope not), the module is gone and needs to
be replaced.

Between the burners is a small rail in the pressed steel where the flame runs across to light the other burners and it sounds like there is dirt or debris in the step over rails causing the problem. You will need to use some compressed air on those rails to clear them out. Once the rails are clear the other two burners should ignite right away.

Flip the lower panel over and look for a wiring diagram. On that diagram there will be a diagnostic chart. Let me know what 5 blinks represent. Then I want you to read on.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the igniter. The igniter will glow and you will be able to see it if viewed thru the small inspection port. Once the igniter gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the igniter does not energize (bad control, bad igniter), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not light (dirty pilot), the burner does not light (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

sounds like the thermocouple that senses when the burner ignites is faulty. when the burner is first lit it looks for a signal from the thermocouple telling it that it has ignition. i have had some luck removing the part (furnace off) and sanding it clean. this is located in front of one of the burners..Good luck

A Make and Model number of the furnace not the thermostat will help but I can walk you thru the operation of a typical furnace. It sounds to me that the burners are igniting properly but the flame sensor is not sensing the flame and shutting down the system. You will need to find the sensor and clean it and check the wire from it to the control board. Typically, the flame sensor is found at one side or the other of the burner box. It is a small probe that the flame hits. Depending upon your model it may have a small wire attached to it leading back to the control. Or it may be part of your auto-pilot assembly. ? At any rate, you will need to get to it and very delicately brush it off. Then inspect the flame channel. This is a trough area where the flame travels to ignite all burners. Over time, they tend to fill with rust and debris. Take a small screwdriver and run the blade down the trough. Inspect the wire that goes from the flame sensor to the control board. Make sure it is not frayed or broken or shorting out and that the connection at the board is good.

Beyond that, it's time for a technician to come.

Let us know the Make and Model of the furnace (found inside the furnace cabinet) and maybe we can help you further.