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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Rick. My name is ***** *****. I'm a licenced automotive tech

Customer Question

Hi Rick. My name is ***** *****. I'm a licenced automotive tech with propane certification, so I'm comfortable working on my furnace. I have a Lennox G20 wth an intermittent delayed ignition concern on the leftmost burner. I have inspected the burners with my borescope camera, and other than a few flakes of rust or plating from the inside of the heat exchanger (no more on this burner than the rest), I see nothing abnormal. I asked a heating guy that services our stuff at work, and he suggested a crack in the exchanger might be allowing a back-draft onto the burner, and where I should look. I can find no cracks or even suspicious hot spots as far as my borescope reaches (about 3 feet). I have watched the burners light about 25 times and that burner is always the last to fire, but usually lights quickly. Occasionally, it may be delayed 2-3 seconds them pops loudly when it does light (maybe 1 in 5 cycles). Once lit, all of the burners look even and have nice blue flames. The cross transfer burners (don't know the correct name) also have even flame and seem to travel to the problem burner in time, yet it seems to light from the back of the burner and travel forward. I see no issues with alignment of the burner components. I took a video with my phone if you would like to see it. I haven't yet checked manifold pressure as suggested by some posts I've found, but I do have an appropriate gauge available. What am I missing?
JA: Thanks. Can you give me any more details about your issue?
Customer: I'm a licenced automotive tech with propane certification, so I'm comfortable working on my furnace. I have a Lennox G20 wth an intermittent delayed ignition concern on the leftmost burner. I have inspected the burners with my borescope camera, and other than a few flakes of rust or plating from the inside of the heat exchanger (no more on this burner than the rest), I see nothing abnormal. I asked a heating guy that services our stuff at work, and he suggested a crack in the exchanger might be allowing a back-draft onto the burner, and where I should look. I can find no cracks or even suspicious hot spots as far as my borescope reaches (about 3 feet). I have watched the burners light about 25 times and that burner is always the last to fire, but usually lights quickly. Occasionally, it may be delayed 2-3 seconds them pops loudly when it does light (maybe 1 in 5 cycles). Once lit, all of the burners look even and have nice blue flames. The cross transfer burners (don't know the correct name) also have even flame and seem to travel to the problem burner in time, yet it seems to light from the back of the burner and travel forward. I see no issues with alignment of the burner components. I took a video with my phone if you would like to see it. I haven't yet checked manifold pressure as suggested by some posts I've found, but I do have an appropriate gauge available. What am I missing?
JA: OK got it. Last thing — HVAC Technicians generally expect a deposit of about $18 to help with your type of question (you only pay if satisfied). Now I'm going to take you to a page to place a secure deposit with JustAnswer. Don't worry, this chat is saved. After that, we will finish helping you.
Submitted: 1 year ago.
Category: HVAC
Expert:  Rick replied 1 year ago.

Have you tried removing and cleaning the burner? check the orifice on the manifold too. From what I can see in the manual it looks like these burners have adjustable air shutters. Could be the shutter needs to be closed down some. Checking manifold pressure is also advisable. Should be 9.5 in. WC for propane 3.5 in. WC for nat gas. I doubt it's a heat exchanger issue. If it was the burner flame would probably distort when the main blower came on.

Customer: replied 1 year ago.
Hi:It looked like a giant pain to disassemble, so I cleaned the burners using compressed air and a shop vac. Borescope shows it did a pretty good job and there's no distorted flames. By the way, in retrospect, your comment about the effect a cracked heat exchanger might make on the flame pattern makes perfect sense. I checked and there are no adjustable shutters installed on this unit, but the provision is there. The manual I have says they are installed as part of an LPG conversion kit. A piece of info I missed is that this is a G20E. It has a Honeywell valve. I've read that some had an issue with the pilot and main valves turning on at the same time. I watched for this on several cycles and found that the pilot always leads the main by about a second, so that doesn't seem to be an issue. I haven't yet checked the pressure as the gauge is at my shop. Is it possible for the main valve pressure to be different in successive cycles? I find it curious that the left most burner ignition ranges from a nice whoosh, to a bang sometimes sufficient to rattle the ductwork. It is obviously getting gas, but the burners light in the order: L/Inner, R/Inner, R/Outer, then a half to full second later, L/Outer with a bang. What could I do to bias the transverse lighter slots on the burners to favour the left side earlier? P.S. I understand this complaint is fairly common on this model and that others have replaced the gas valve and burners without improvement. I'm not one to throw parts at something. Your experienced opinion would be appreciated! Thanks Much!
Expert:  Rick replied 1 year ago.

It's possible that manifold pressure could fluctuate in a failing valve. The burners can only light in succession starting at the one with the pilot. You said the crossovers looked good so that leaves an obstruction in the burner as a likely culprit. You have to remove the burner to properly clean it.