Okay, what is going on. is the system lighting or not. If it is just sparking then you need to just the gas value. But if the system lites and then only have a flame for about five sec. then shuts back off, then your flame sensor is dirty. Take a wire brush and clean the flame sensor. The flame sensor is right there with the burns because a flame has to hit it for the gas to stay running. Just take a wire bush and clean it..... let me know
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Troubleshooting and Repair Furnaces with electronic ignition systems
may be much more efficient than their early counterparts, but they do it largely
through electronics. However, there are still some troubleshooting you can do
but fixing the problems can involve replacement of parts more so than repair or
PROBLEM: Furnace burner will not ignite
With a Hot Surface Ignition (HSI) system, if a gas hissing sound is
heard for about 7-10 seconds and the burners do not ignite, the furnace will go
into lockout mode.
To reset turn the furnace power switch off and back on and try again.
The switch is probably located on the side of the furnace. A reset button may
also be found on the solid state controller. If resetting fails again, proceed
Turn off power and gas to the furnace
Remove and check hot surface igniter being careful not to touch the heat
element. If it is cracked or damaged, replace the igniter.
PROBLEM: Furnace comes on for 7-10 seconds then turns off
Turn off power and gas to the furnace
Remove flame sensor from its bracket. Lightly clean the surface with fine
emery cloth and replace.
The problem may also lie in a bad ground or the the black and white wires
being reversed (reversed polarity) at the junction box or outlet powering the
The electronic ignition control module must ensure current flow through the
flame sensor to ground and if the polarity is reversed in the circuit there is
no voltage potential and the flame sensor does not work and closes the gas
If the black and white wires are connected correctly and the flame still
drops out, then the issue may be a bad ground. Using a volt-ohm meter, measure
between the white wire and the ground wire to be sure you have no voltage.
Yes there is a sequence: 0:00 Dial for fan/limit switch is at 70 deg position. Furnace is cold. I turn T-stat to 80 deg to start furnace. 1:00 Burner comes on and dial begins to move slowly up. 2:30 Dial at 140 deg and fan motor comes on. Dial never goes above 150 deg. 3:00 Burner turns off. Dial slowly moves back towards 90 deg. 4:45 Burner turns on and dial is at 110 deg. 4:50 Fan turns off with dial still at 110 deg. 5:30 Burner off. Dial at 120 deg. 6:15 Fan on. Dial at 140 deg. Burner is still off. 7:00 Burner on. Dial at 120 deg. 7:40 Burner off. Dial still at 120 deg. 8:30 Fan off with dial at 110 deg., and it quickly snaps back to the 80 deg. position. 8:30 plus, cycle continues.....
It sounds like the last 2 burner pilot cross lighters are either dirty with rust or they are out of alignment.You need to remove the burners then wire brush the ends of the burners and cross lighters and make sure the burners are level with each other. Hope this solves your problem!!
I have serviced these furnaces for 20 years and I can tell you most of these models did not have diagnostic lite on them. (although some did, especially if the control board has been replaced) The problem is most likely a bad 3 wire pilot. This will cause exactly what you describe. 2 things to consider though. 1, If you were to replace the pilot don't get a cheaper knockoff. In my experience these do not last long at all. Get the right one from a carrier dealer. It will cost more but be much more reliable. 2 What is the condition of the secondary heat exchanger? Most if not all of the sx series had issues with the secondary heat exchangers rotting out and leaking. If the furnace is out of warranty you would be much better replacing the furnace as the cost of replacing the secondary heat exchanger will probably be almost the same as a new furnace. ( those babies are EXPENSIVE!)