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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a Lennox L.P. furnace. Ser.l # 5881GO3611, Model #

Customer Question

JA: Hello. How can we help?
Customer: I have a Lennox L.P. furnace. Ser.l # 5881GO3611, Model # G1203-110-3, input 110,000 btu's.
JA: Did you check the furnace's filters?
Customer: My problem is that occasionally when it lites, it does so with a very noticeable report-boom etd. If you are standing near the unit with the cover off a flame will shoot about 2 feet and then go ahead and lite and burn normally, at least most of the time. Sometimes when if flashes like that then when it lites in one or more of the burners a flame will be next to the air adjustment on the burner. The preassure is set at 10.5 inches and the adjustment screw won't budge. When it's burning correctly it puts out good heat and most of the time does so without a boom. I think thats about it.
JA: Do you plan on doing the work yourself?
Customer: Yes
JA: Anything else we should know to help you best?
Customer: What do you think causes the boom etc.
Submitted: 9 months ago.
Category: HVAC
Expert:  gotoman for ac replied 9 months ago.

Russ here you have a delayed ignition. The pressure on valve is ok. Need to clean the burners. Where the burners connect across. Need to take a wire brush and clean across burners at top.. Make sure all of them line up. The top of burners is where the flame runs across to lite. If it is a little dirty it will cause the problem.. If cleaning does not help you will need to replace burners. May be to corroded. Russ