furnace troubles

[t-bone]

I have a 75,000 btu input Arco Air gas furnace that was converted to LP gas when it was installed in 2000 that wasn't working properly. I went out on the call and only one of the burners would light. I noticed that the three burners were all carboned up. I cleaned the burners and the thing lit all three of them. As it ran the flames would occassionally creep back into the burner assembly. But it wasn't really a lazy flame like a venting problem. It would just creep back into the mixing chamber periodically. I checked the gas pressures inlet and outlet of the gas valve both were good. ( 12 in wc inlet and 10 in wc outlet). I disconnected the vent pipe but it did not mater. I am suspecting maybe a small crack in the heat exchanger just enough to effect the draw of combustion gas into the heat exchanger but I am not sure. I was hoping that you guys might offer some insight.

[Peter_1]

I don't think that you will see replies to a post of burners in a refrigeration forum.

[momo]

Check out h__p://___.hvac-talk.com/vbb/
on your side of the water... plenty to read there.

[Karl Hofmann]

I can't comment on the equipment that you are working on as we don't have this make of kit, but if any of the burners are carboned up, the you have a serious ventilation problem that needs to be sorted out, the air supply is not enough for the furnace input

[t-bone]

Thanks for the info Karl. I talked with the manufacturer and they thought that I should replace the gas valve. They stated that moisture could settle in the valve and small particles of water would enter the mixing chamber and cause a sputter and allow the flame to enter the chambers causing the black soot. But I think you are correct about the combustion air lacking causing the black soot because air would be lacking in the chambers. Thanks again for the help.

[t-bone]

Check out h__p://___.hvac-talk.com/vbb/
on your side of the water... plenty to read there.

Thanks for the info. I will check it out.