Burner will not fire

It could be the fan motor capacitor

SOUND LIKE FAULTY THERMOSTAT.FIRST CHECK TO MAKE SURE YOUR CAR HAS ENOUGH COOLANT IN THE COOLANT SYSTEM.FAST WAY TO TELL YOUR THERMOSTAT BAD.BOTH RADIATOR HOSES SUPPOSE TO BE VERY HOT.IF NOT THERMOSTAT STUCK CLOSED NOT ALLOWING COOLANT TO CIRCULATE FROM ENGINE TO THE RADIATOR.IF THERMOSTAT IS FAULTY.REPLACE THERMOSTAT AND RADIATOR PRESSURE CAP.

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).

If the room air blower is blowing air but not warm, it is an indication that there is a problem with the unit and an error code is blinking on the board. To view the code, look thru a small viewing port in the lower panel. Count the blinks and then find the panel that has the wiring diagram glued to it. On the diagram you will find a diagnostic chart to correspond with the number of blinks.

This may also help:
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).

Bad or dirty flame rod or burners.

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).

There will be a separate pressure switch for hi fire, make sure all hoses are connected and free of moisture and debris. You can temporally jump the switch once the inducer fan speeds up, not before. If the unit fires on high, you have a pressure switch issue. If the fan does not speed up, you may have a bad relay on the control board. If the unit is just being put into winter service, it may have a cob web restricting gas flow to the burner. You will need to check the air inlet as well as the exhaust pipe for restriction. Check on the wiring diagram to make sure that the DIP switches are in the proper position, you never know. Hope this helps.

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).

I have this clunker-4 flashes is an open high limit code according to the wiring diagram and fault code sheet. the common denomonator for this furnaces problems is the circuit board. Always flashing 3, 4, 7 times most of the time having nothing to do with the problem. The actual problem is the board it's self. take it off the mounts (POWER OFF FIRST AND SWITCH OFF>)
remove from the 4 mounts one at a time then check the back of the board. you will probably notice brown spots on the green. this is where the board has burned up. replace the board and you will be fine, you will also be the 100th person I know to have this problem. Make sure you take a picture of the board before you take all the wires off so you can put them back properly. I personally have replaced the board twice the first replacement I purchased (warranty) was made by the same company as the original, the second board I replaced 1 year later with a new board made by a new manufacturer. they obviously knew there was a problem.

http://hphotos-snc3.fbcdn.net/hs066.snc3/13331_1198507328519_1403584043_30566732_3667503_n.jpg

this is a picture of a board another fixya user sent me today after he had the same problem as you and I told him what to look for. look familliar?

If you are getting fire and have an eo5 this is a reading for no flame so it is not reading the flame. What you probally have is small spider webs in your burner orfaces. You will need to pull the burners out and with a small wire or the like clear the gas orfaces going to the burners. These little webs can divert the gas to the main burners and keep it from the burner that reads the flame. Your heater will come on with a big woosh as the gas needs to come from other burners to fire. I hope this helps. Good luck

test thermostat: turn on heater...is there plenty of heat blowing?
if not, replace thermostat.
if yes, then replace coolant, but flush cooling system before new coolant goes in.