Furnace burner blowing back ?????

5 year old, Bryant 94%, model 355AAV042080, on propane.
Bryant tech was out last November to clean burner orifices, adjust propane pressure - seemed to be OK.

Yesterday I got the ignition lockout code (means it didn't light properly). The burner (1 of 4) which flames on the ignition sensor was burning yellow, and the flame sensor was sooty.

Today I cleaned the flame sensor, and the burner orifice (the other 3 were clean). Forced it to run on propane (not the heat pump) and watched several ignition cycles. The ignition sequence seems OK - induction fan starts, ignitor glows, valve opens, and the burners catch on.

However, the burning startup doesn't seem "smooth". It used to light at the ignitor, then travel across the 4 burners in order. Now it sorta lights all at once - a "POOF". Often some of the burners will flame back to the orifice in the manifold - and burn about 1/2 yellow. If I blow it out (with my mouth) it'll relight at the burner orifice and burn nice and blue.

When its burning, I can feel the exhaust flow outside at the vent, but I'm not experienced enough to know if its as strong as it should be.

Sure would appreciate an experienced furnace tech tell me what's gone wrong - or what I need to check further.

Check the exhaust pipe out side to be sure in is not restricted by snow or something else.

Check the exhaust pipe out side to be sure in is not restricted by snow or something else.

I've sold and serviced Bryants for years, with it being on propane, the burners may need changed. The propane we buy today has alot more moisture and inert matter in it than it used to, causing rapid deterioration of the burners. If not replaced the burners will continue to get worse as far as burning dirty and sooting up. This soot will plug up the secondary heat exchanger as well as the primary. You can check the exhaust pipe outside to see if there is any soot on the inside of the pipe, if there is you may have big problems already. If the secondary heat exchanger is sooted up already, you cant clean it, it will need to be replaced. If its not covered under the warranty, dealer cost is between $750 and $1000. Sorry all doom and gloom, you better get a tech out there to check it out.

Check or replace the two regulaters outside of the house!!! If there old they could have rust and not giving the right gas preasure

Your heat exchanger is cracked in that burner chamber! When the power ventor motor runs it causes a downdraft situation with that burner. I had a furnace last fall doing exactly the same thing. Dave

At the very least you have a partially or fully plugged up heat exchanger, and at the worst the secondary is also in the beginning stages of plugging.

The yellow flame means there is not enough combustion air mixing with the fuel to burn correctly. Yellow flame equals excess carbon which is what is plugging up the heat exchanger blocking yet more airflow creating more and more excess carbon. Left unchecked this thing will plug totally or hopefully open the pressure differential switch and shut the system down and lock it out.

You must get a qualified service tech on this issue as soon as you can, it may not be too late to have a reasonable repair cost...but trying to operate it much longer and you can kiss goodbye just about any money the high efficiency has saved you for the last couple of years !!!!!!

Just a thought, I would also worry about carbon monoxide poisioning, to say the least.