Goodman GMT045-3A Furnace. Furnace flue fan always on, glow plug hot, gas ignited, on for 20-30 seconds, click is heard, flame off, glow plug cools. Then cycle repeats over and over again. Sometimes blower comes on. Thermostat on 55, outside temp is 16 degrees. Taken flame sensor out and tried to polish it up. Did not have sand paper. Looks like there may be a crack in flame sensor side. I am thinking about replacing flame sensor as a start.

Clean your flame sensor with soft wire brush. It is located opposite side of igniter. Builds up with glossy coating and doesn’t sense the flame so it shuts off the gas valve

This happened to me where the glow plug was working but couldn't hear the gas valve click on.
I tapped on the relay w channel locks and the gas came on, Flame on!

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.

Hi,
The problem you have is water in the exhaust pipe.
Check to see if the pipe has sagged anywhere or if there is a trap in the line.
If you hear gurgling then it is definetly water....
Some times can be hard to find, even a pipe 1/4 full will cause problems. They are very sensitive to flue problems.
Make sure that the flue pipe either runs back to the furnace or out to the outside, a continuos slope either way witha high spot in the middle.
Also check the bottom drain of the blower if it has one, have had them plug and trap water also..

I hope that this will help you to solve your problem!

Thanks for using Fixya!!

Heatman101

The sequence of events for furnace operation is -

Fan purge for 30-45 seconds. During this time, a pressure switch is actuated by the running of the purge fan, proving the control board the purge fan is running.

After purge and purge prove, the hot surface ignition and or spark begins. After a few second delay, the gas valve will open. The control board then monitors for flame prove through another sensor located near the burners. If there is no flame within 3-5 seconds, the gas valve closes. It will repeat this process, usually 3 times, before it shuts the system down, which requires a power down of the system to reset.

I have seen trash get into the hose between the purge blower and the purge switch. But you could be having other problems.

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 is a chart with the wiring diagram and othere charts that will tell you what the 6 blinks are for. That should tell you what is wrong and what part you need. Sounds to me like the board has an issue or the gas valve is locked out.

bad board,i have had several board failures on goodman

If in fact you have the above listed furnace, you do not have a pilot but electronic ignition. You will need to remove the front cover on the furnace, tape down the door safety switch and then have someone help you by turning up your thermostat to a very high setting. Watch and listen inside the furnace. There should be some blinking going on at the control board followed by a small blower fan starting up. Then after 10-15 seconds there should be a click followed by an orange glow viewed thru the viewing window to the burner section. In a few seconds the gas valve should click and the burners will ignite. There is a safety switch that will sense flame and then keep the gas going to the burners. If it does not sense it, it will shut it off within 10 seconds. If all is well so far, your blower will turn on in about 90 seconds after flame. There is a diagnostic code chart on the back side of the access door if you get an error code (blinking) on the control board.

Always check little things like air filter, condensate drain and broken or loose wires.

try cleaning the burners and or adjust the distance the igniter is from the actual burner .