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Thread: Armstrong Air Furnace - Failure to Ignite

  1. #1
    Join Date
    Sep 2016
    Posts
    2

    Default Armstrong Air Furnace - Failure to Ignite

    I have been having issues with my furnace failing to ignite for a while. I have both cleaned and replaced flame sensors, as well as replaced the control board. I have checked the FLA on the induction fan motor, meter out all control switches and even gone as far as to pull out the heat exchanger and clean it. The combustion fan moves adequate air and there aren't any obstructions in the exhaust.
    The furnace will fire sometimes but more often than not it tries 3 times and locks out due to a failure to ignite.
    The burners will light but won't stay lit. What are some possible causes for this besides the flame sensor being oxidized (it's new and clean, as is the control panel)? Could it be a fuel mixture issue? Safety valve?

  2. #2
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    238

    Default

    Probably time to call someone out. I know that's not what you want to hear.... It's often cheaper then throwing random parts at it and risking creating additional problems.

    "moves adequate air" There is a specific amount. It is often measured in negative pressure (vacuum) generated by your inducer. There has to be enough to satisfy the pressure switch. Just "moving air" may not be enough. Have you checked the vacuum hose for obstructions or cracks, and if the pressure switch holds a vacuum? An obstruction could be in the inducer too. Just takes a curious bug....

    Is there sufficient flame AT the flame sensor? A dirty burner could give you a healthy flame in some areas but not another. There might be flame at the sensor, but is it hot enough produce the proper output on the flame sensor? If your flame sensor did fail or get dirty to the point it wouldnt function, that indicates you may have a combustion issue. There may be a position adjustment on the sensor bracket, or the bracket could be bent.

    I am assuming that if your furnace has a status LED on the control board, that you checked for a code being flashed out and looked it up.

    If your furnace has adjustable air mixture shutters, they adjust for a clean mostly blue, stable flame. They are adjusted by sight and don't normally need adjusted unless something significant has changed. They shouldn't be adjusted to compensate for a dirty burner (unless they have already been disturbed). I doub't that you can move those out of adjustment enough to make the furnace not run. Adjusting them wrong WILL create excessive carbon monoxide (a silent killer)

  3. #3
    Join Date
    Sep 2016
    Posts
    2

    Default

    Thanks for your speedy input Mr. T. I should elaborate.
    I have already had two different contractors out to look at this furnace, all limit switches tested (I'm an electrician myself) and burners jets cleaned. Here's the kicker, if I remove the cover from the combustion chamber it ignites and runs properly every time, even after I replace the cover.
    This makes me believe it is a fuel mixture problem. Could the orifice in the gas valve be washed out (natural gas)? Also, when the furnace fails to ignite and cycles five times before lockout there is a strong natural gas smell in the utility room. Leads me to believe the furnace is oxygen starved at time of ignition (too much gas vs o2 pulled by combustion fan).
    Thoughts?

  4. #4
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    238

    Default

    Is there an outside air intake? There is usually nothing to check if this is blocked, other then no air flowing through the inducer to trip the pressure switch. Can you see the flames when you put the cover back on? Does their properties change? Do they change color (blue goes away), do they get jumpy or 'lazy'? These are signs of potentially dangerous air issues.

    There are no mixture adjustments like an engine has. The shutters you may see are mostly there for fine tuning.

    If this furnace is in fact starved for air, then you need to be very careful. This will cause incomplete combustion which increases the output of carbon monoxide (a silent killer). If you fix this yourself, PLEASE have someone test your Co levels. Many gas companies and fire departments will do this. If the levels are not safe, they will red tag the furnace. Still better then being on the news...

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