Suburban Furnace SF-30F year 2006

[thirteen]

I am having problems if anyone has any suggestions.
No problem with blower running. Thermostat switch is functioning.
I turned on all three stove burners and cooked with nice blue flame and no yellow so I am getting nice gas pressure.
I took it apart and adjusted igniter. Before putting it back together I tested it and the spark is very good.
I turn the thermostat to 90 degrees and fan runs for 15 seconds as expected then igniter goes but it doesn't light. It goes through I think three cycles.
When I took it apart I tested it before reinstalling and it ignited and got hot enough I had to shut it off as it was sitting on my carpet and exhausting inside.
Maybe I didn't wait long enough for full test but it was too hot outside of the housing.
I reinstalled and not igniting. It has good gas ( I can smell it as well), no air intake or exhaust obstructions, fan runs strong and igniter works.
What do I check next?

[thirteen]

Maybe blowing out the propane tube helped. Maybe bumping the electrode put it into the correct place. Right now it is working well. When I get home I will take it out again and with a workbench I will go over everything I learned today. I will make sure all connections are good and use electrical tape and zip ties. It seems like a Chinese fire drill so far so it isn't very comforting.

[Chris_Bryant]

I wrote:
Other than electrode placement, I usually find this is a partially clogged orifice. With just a bit of rust in it, propane will flow, but not enough to reliably ignite.

[thirteen]

New development. I get spark most of the time now and it is firing up. Is this because the electrode is not perfectly aligned?
Is it possible sail switch is only working sometime?
This new development is after I opened it up and at least bumped the electrode.

[Old-Biscuit]

IF board was bad you wouldn't get any voltage to spark electrode and gas valve.

Good spark and gas valve opens..then spark has to be out of position or burner assemble is out of alignment.

[thirteen]

I opened again and there is great spark. I measured per the manual and put the igniter exactly where it is supposed to be. I left the pipe to burner off and ran it and propane Valve opened and sent gas into air. I checked the temperature sensor and bypassed it and no change. I tested DC voltage and it is good. So if there is spark and that means sail switch is fine then the only thing I have left is the control board?
Doesn't make sense that I have spark and gas but no flame. I checked gas tube to burner and I can blow air through it.

[Old-Biscuit]

If you are getting a spark but no main flame but gas valve is opening then the spark electrode is out of position....electrode must be engulfed in main flame in order to send signal back to module that 'I am lit'

Gas valve & spark electrode get voltage at same time....but only for 7 seconds to gas valve.

SF Service manual..........pg. 37 describes proper positioning....LINK

[Chris_Bryant]

The fan control boards do sense a bypassed sail switch- it knows if the fan relay is not engaged, the sail switch should be open.
Other than electrode placement, I usually find this is a partially clogged orifice. With just a bit of rust in it, propane will flow, but not enough to reliably ignite.

[enblethen]

Ig nitor opreates then the sail switch is operating.
I would look closely at the positioning of the flame sensor which is the same as the ignitor.
Verify that you have good 12 volts DC at the furnace.

[thirteen]

I tried to bypass the sail switch but it only hums. Not sure what that switch does that I can't bypass it unless the circuit board can tell I bypassed it.
Looking in I don't see spark anymore. I have not taken it apart again to verify no spark but can't see any through sight glass.

[Ka_Ron]

Check the sail switch.
This is a proving switch that ensures there is proper air movement to light the burner.
If it fails the burner will not light