I have a dependable 92 furnace that will not light. I have cleaned the flame sensor and that didn't do it. I can hear the click like it is trying to light but no flames. After it tries to light 2

SOURCE: my burner goes on but shuts off early

First when it goes out again, locate the furnace and look thru a small viewing port to see if there is a light blinking, count the number of blinks. Then look at the wiring diagram for a diagnostic code chart. This will give you a strart of where to look.

SOURCE: How do I clean a flame sensor on a 1993 Lennox

You can sand the flame sensor but it sounds like another problem. Sounds like a limit switch or something in the control circuit, You need to have a service tech look at this. Ask for free estimate on repair. I have worked on hundreds of these units and they are sometimes tricky to work on. Lenox has come up with new controls for the whisper heat furnace to replace the old ones. If the flame sensor is bad the unit will try to light a few times and lock out and you ahve to kull power to the furnace to reset. If this is whats happening clean the sensor nd you should be ok If not you need help from a service tech.Rus

SOURCE: FURNACE COMES ON AND SHUTS DOWN WITHIN 15 SECONDS

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). When all else fails, check the ground connection for corrosion.

SOURCE: Gas furnace; flame will not stay on

Clean the flame sensor with a green scotch brite pad. Check all ground connections from the circuit board to the furnace cabinet. Check for a proper ground to the electrical box. Make sure polarity has not been reversed.

SOURCE: I have a goodman gpmn

Hello, looks like you limit switch keeps opening because your furnace is overheating, Check your air filter and blower wheel to make sure it is not dirty and make sure you blower motor is moving at the proper speeed. Usually when air flow is cutoff the limit switch will open.