WONT HEAT. BLOWER COMES ON BUT NO HEAT. IT HAS NO

Check and see if pilot is on

try to change capacitor

Make sure the blower access panels are on firmly. There is a safety switch on most gas furnaces that will prevent operation in the event the blower access panel is not on or loosened. Also make sure a power switch (sometimes looks like a light switch) was not accidentally left "off". :-)

I hope you find this to be very helpful moving forward.
:-)

If the blower access panel is not the problem, let us know and we'll dig deeper. :-)

Check for 24 volts across the gas valve when Ignitor is glowing. If no, bad board. If yes, bad gas valve or blockage.
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).

Tie red and white wires together after removing thermostat from wall, if unit comes on replace thermostat, if not check limit controls for continuity, Good luck.

This sounds like the high temperature switch has failed and is telling the unit to shut down after it gets started, the pilot has to be lit for the main gas valve to turn on when the thermostat calls for heat, The main burner comes on and stays on until the thermostat is satisfied and tells it to shut off, you dont say if there is a blower in this unit, if there is a blower after the main flame comes on the unit heats up it turns on the blower if equiped. If the blower fails to turn on the unit would be shut down on overtemp as the firebox would get to hot and be in danger of causeing a fire. if no blower there still is an overtemp switch that shuts the unit down if it gets to hot or the switch is bad, it could be a bad overtemp switch or if equiped a bad blower motor or even a plugged chimney as this would also cause a overheat ing condition. Hope This Helps Don

i think the ca # is for the cooling coil unit - the heater should start with gmXXXXX - if your unit is fairly new - the pilot light electronically when thermostat calls for heat the unit will not light if the burner door is open

If the unit is newer than 10 years I guess there will be no pilot light per sey. You will have to look at it to tell for sure. Here it is supposed to work. When there is a call for heat the thermostat will close and send a signal to the furnace to start the exhaust blower. When the blower gets up to speed, it closes a pressure switch that will send voltage to the gas valve and to the igniter. The igniter glows or sparks lighting the pilot. Once the pilot lights it sends a signal that all is well, then the gas valve opens up more and the burner(s) light. There is a sensor that tells the control board when the flame has stayed lit. Once that is done, after a period of time or as the heat exchanger gets to a specific temperature, it will turn on the room air blower and blow hot air. Once the thermostat has been satisfied, the furnace turns off. Now, get in front of the furnace and with the door panels off (you may need to tape down the door safety switch to make this work) watch the furnace go thru each step I described. Once you see where the problem is, you can start the proceed of repair. There may even be a flashing light indicating a problem. Find the wiring diagram on the furnace and look for a diagnostic chart and compare the number of blinks to this chart.

Hi

If it won’t fire then it is possible that the oven control is not sending gas for the pilot light. The pilot light works but no main burner ignition - possible pilot assembly is dirty and the pilot flame is too small, safety valve and thermocouple is faulty, the bulb from the safety valve is out of position and the pilot flame is not touching the thermocouple bulb. Some ranges use a standing pilot light ( small flame is on all the time ) while others use an spark ignition to light the pilot light flame and the pilot light flame heats up the thermocouple bulb to allow the main gas to flow through the oven burner.
The flame needs to heat the bulb up enough to tell it to open the gas valve. Several things can go wrong here that keep this from happening:
The pilot flame may not be hot enough, usually because the flame is yellow instead of pure blue or is too small. The cause for this is usually a dirty pilot assembly. The pilot assembly would either need to be cleaned or replaced.
The thermocouple bulb may not be positioned properly in the flame. You can't heat the bulb properly if it's not in the pilot flame! The thermocouple bulb needs to be in the upper third of a pure blue pilot flame--that's the hottest part of the flame.
The thermocouple itself may be burned out. It happens. It's an internal part of the gas valve so, no, you can't just change the thermocouple bulb separate from the gas valve.
But when you turn on the oven or the thermostat calls for heat, the pilot flame gets bigger and jumps down so it can heat up the thermocouple bulb. This extra gas to increase the pilot flame size comes from the thermostat.
If the pilot flame jumps upwards or just gets bigger, but doesn't shoot down, then you need to replace the pilot assembly.
If the pilot flame size does not increase or jump down when turning on the oven thermostat, then the problem is the thermostat not sending enough gas to the pilot assembly. It's also possible that the pilot gas supply tube has a hole in it somewhere.
One final point on the spark-assisted pilot ignition systems. The spark comes from the spark module--the same module that sends spark to your surface burners to light them up. If you're not getting a spark when you turn the oven on, then there are several possibilities:
There could be a problem with the switch in the thermostat. You can confirm this by doing a simple continuity test of the thermostat contacts. If you don't read zero ohms when you turn the switch on, replace the thermostat.
The spark module could be bad. You'll need to measure the voltage at the oven terminals of the spark module when you turn on the oven. If you get 120v but no spark, it's probably a bad spark module. Replace it.
Could be a bad spark wire or broken electrode.

Please do rate the solution and revert for further assistance.


Thanks
Rylee

The pilot light has to be lit before gas valve will operate. That's a safety feature so the valve won't open and fill the garage with gas and possibly cause an explosion or fire. If you have a standing pilot and can't get pilot to stay lit, it's usually the thermocouple and it will need to be replaced. Once the pilot is lit, the gas valve comes on and heats the combustion chamber up to approx. 100° to 125° a thermostat controlled fan switch will close and bring the blower on.