Coleman furnace

[kdickman]

I have a 7956-856 propane furnace. The burner does not light want to light properly every time the thermostat kicks on. I had a technician look at it. He replaced the pilot and the thermocouple, and also said the roof jack needed replaced. I have since replace the roof jack and the problem has gotten a little better, but it still is not corrected. I think that there is still some debris from the old roof jack inside the exhaust port at the burner chamber, but I can't figure out how to get to it without completely dismantling the furnace. I can feel up in there through the burner chamber, but I can't get to it with a vacuum. Will the furnace work itself out of this or does that have to be cleaned to restore proper air flow?

Kevin

[hvac1000]

If something is in the furnace/roof jack area that does not belong there remove it. It will not work itself free to the best of my knowledge. You said the burner was not starting correctly but no details on how you know this fact or exactly what it is doing? How about a little detail on the burner light off problem.

[kdickman]

Once the thermostat kicks on, the burner will either do one of two things. It will light within a few seconds as it should or it will take around ten to fifthteen seconds to to light. When the burner does not light right away it generally blows itself out and the pilot along with it making a loud poof sound. I know this from watching through the burner window. The technican explained to me that this was happening because the airflow was restricted from the roof jack rusting out and the proper propane to air mixture was not being achieved. I have since replaced the roof jack and the problem is not as frequent, but is still occuring from time to time. before the new roof jack was installed this was happening every two or three time the burner would light. It is now happening once everyday day or two. There are only small rust particles in the exhaust tube of the furnace, nothing off any size or shape that would obstruct air flow.

[hvac1000]

It could be as simple as a adjustment to the air over the burner or a gas pressure adjustment. You will need a pro with the proper tools to check these items. Intermittent problem are always the worst to find but with the proper tools at least the items above can be checked to make sure they are within specifications.

[kdickman]

Thanks for the reply, I will let you know the outcome.

Kevin