Furnace Ignition Question

[ILVMYGT]

I am helping a friend troubleshoot a Suburban LP furnace. When the furnace starts it take several ignitions cycles before it stays running. The furnace "lights" for a fraction of a second (a puff of warn air) then goes out, then "lights" again. It takes several of these cycles before it stays running. You can hear the gas solenoid click turning on the gas. As best we can determine once the gas is on it stays on. The Sail switch is also working since the gas and ignition is turning on. Is it normal for it to take several ignitions cycles for it to stay lit?

[Bigdog]

garry1p wrote:
May be no help but;

I had a similar problem and found it was air in the line.
Would work fine if a stove top burner was lit at the same time as lighting the furnace.

Only happened 1st few times at beginning of winter use "and" the propane tank had been refilled.

X2, mine will do that if it hasn't been used for awhile. It's only the front one and I also turn on the water heater gas and the stove top and get propane up to the furnace. It seems as if the stove is the last item on the line.

[ILVMYGT]

Thanks to all. The manual enblethen provided had some great troubleshooting information.

[John_Joey]

dougrainer wrote:
The burner Jet(orifice) should ALWAYS be removed and checked and cleaned out ...

Given the age of the furnace this now would be my very first guess. Issue you will have is the gasket will fall apart on you when you go after the jet. Very carefully pull it apart to save as much as possible.

[kedanie]

Another possibility is the propane regulator may be full of oil restricting the gas flow. Simply remove it and turn it upside down or move it around and if oil comes out of the vent then a new regulator is needed.

Keith

[garry1p]

May be no help but;

I had a similar problem and found it was air in the line.
Would work fine if a stove top burner was lit at the same time as lighting the furnace.

Only happened 1st few times at beginning of winter use "and" the propane tank had been refilled.

[dougrainer]

ILVMYGT wrote:
The burner was removed, cleaned and blown out with compressed air. While the burner was out the inside of the "combustion chamber" was vacuumed out.

The connector for the electrodes and gas solenoid at the control board was cleaned. While starting the little bulb on the control board flickers when the electrode sparks.

The electrode was replaced with a new one with the correct gap. Before reinstalling the electrode the high voltage wire was connected to it and spark was verified.

This is an older furnace (1993). A review of the schematic there does not appear to be a separate sensor that detects the flame.

The burner jet has not yet been cleaned. But you can get slight gas smell when it first starts.

The burner Jet(orifice) should ALWAYS be removed and checked and cleaned out when accessing the burner. If a microscopic debris is in the gas valve/orifice area. it can be "pushed" outward and restrict the LP flow. You need to do this before proceeding further. Doug

[Old-Biscuit]

The flame sensor is part of the spark electrode assemble

Not only does the gap have to be correct (1/8") but the electrode also has to be directly in flame path (engulfed by flame)

Gas valve and spark electrode get DC voltage at same time.......gas valve only gets voltage for 6-8 seconds during ignition then IF main flame does not light off and PROVE it circuit board drops DC voltage to gas valve closing it.
The millivolt signal generated by main flame is what circuit board needs to keep gas valve open. If electrode is not engulfed by main flame or is dirty the signal can not go back to board

[Kayteg1]

Those things do have several sensors and are not that easy to troubleshoot.
Newer boards have LED that will blink giving you error code. Do you have one of those?
Beside flame sensor you also have at least 1 overheat sensor, that will cost the flame go out.
How about some pictures?

[enblethen]

This manual may help.
Suburban manual from Bryant RV

[ILVMYGT]

The burner was removed, cleaned and blown out with compressed air. While the burner was out the inside of the "combustion chamber" was vacuumed out.

The connector for the electrodes and gas solenoid at the control board was cleaned. While starting the little bulb on the control board flickers when the electrode sparks.

The electrode was replaced with a new one with the correct gap. Before reinstalling the electrode the high voltage wire was connected to it and spark was verified.

This is an older furnace (1993). A review of the schematic there does not appear to be a separate sensor that detects the flame.

The burner jet has not yet been cleaned. But you can get slight gas smell when it first starts.

[dougrainer]

No, it should light on the first of the 3 attempts. From your description, the Spark electrode is probably NOT at the correct gap. Doug

[enblethen]

What is the model of your Suburban furnace/
It could be dirty contacts on the circuit board connector.
Furnace may need cleaned and the electrodes adjusted.

[John_Joey]

ILVMYGT wrote:
...snip... Is it normal for it to take several ignitions cycles for it to stay lit?

I would say no. My best guess is the computer is not sensing a flame and it takes a few attempts before things heat up enough where it does. If it was me, the first thing I would do is clean the high energy wire to the sparker on both ends.

On Edit:

While I had that wire off I would also take out my meter and check to make sure it has good continuity. Flex it a little while watching the meter. Very possible it might handle the high spark load, but loose a little too much in the flame sensing ability.