90+ Gas Furnace Flame Sputtering

[cp3]

I was working on a Trane gas furnace. As soon as the burners ignite they come on and off very rapidly. Here’s the sequence: the inducer starts, the HSI glows, and the gas valve opens and then the burners ignite and they sputter on and off very quickly sometimes they catch and sometimes they don’t. The blower isn’t running at the time this is happening and I did inspect the heat exchanger and couldn’t find any cracks. What would cause the flames to sputter very rapidly? Thanks for the help

[David Goodman]

What were your inlet and manifold pressures?
Were they stable?
Was this a positive or negative pressure valve?

[rundawg]

If you are a tech as your profile states, you need to have this thread moved to the "Tech to Tech Chat - Residential" forum. This forum is for homeowners to ask questions.

Click on the small black triangle near the "like and Dislike" tabs at the bottom of your thread, and ask to have it moved.

Once moved, please provide the Model and Serial number of the unit, and answer the questions asked by "David" above.

The more information you provide, the more guidance you will receive.

[cp3]

I don’t have the whole model number. I know it was a XT95, single stage. My incoming pressure was 7.4” WC and my manifold pressure was 3.6”WC. My manifold pressure would be stable until the sputtering would happen, then the pressure would drop out. The whole time my incoming was steady

[pecmsg]

What does tech support say?

[beenthere]

Moved to tech to tech.

[cp3]

I sent a request in to move to tech to tech

[rundawg]

My manifold pressure would be stable until the sputtering would happen, then the pressure would drop out. The whole time my incoming was steady

Does the voltage to the gas valve stay constant when it starts to sputter?

Does the unit ever light and gas flow stabilize?

[cp3]

Every time the burners sputter the voltage drops. Sometimes after the burners sputter they stay lit and sometimes they don’t. When they don’t, the inducer starts again and the furnace tries to fire again. There is no error code. When the burners stay lit there is a constant 24v at the gas valve

[theoldscroll]

What about draft pressure? Switch could be cutting in and out but doing what it's supposed to. Drainage issues, dirt in the port? Troubleshoot it, eliminate what it is not.Could be a voltage drop thru a thermo-disc type limit like I say about a week ago.

[Kennyhvac]

If there is no error code i would start with checking the thermostat. Everything in the furnace that will shut it off will or should give a code and lockout.

[theoldscroll]

If there is no error code i would start with checking the thermostat. Everything in the furnace that will shut it off will or should give a code and lockout.

Not always bro. As I posted about a week ago, had a thermodisc rollout switch with enough resistance to drop voltage thru the circuit to "sometimes" not power the gas valve. Didn't show up as rollout or limit fault. only shows up as ignition failure. Would work about 20x or more following or go for weeks. Finally got to doing it enough to catch it. I assisted another tech who had been there multi times (a GOOD tech mind you). Some of these humble you but it makes a good tech out of you. The OP here just hasn't done enough troubleshooting yet before askin' for somebody to tell how to fix it. I love the "nuggets" I've gotten here on this site. I am not a fan of our next generation of entry level techs (some not all), who if it ain't starring you right in the face they pull their cell phones out and look online. Good technicians have had their nose bloodied, butts kicked, dragged around on the pavement,and took every step needed, all to gain that knowledge and earn the title of service tech. Some of today's kids just want to find the elevator to the top. "I don't want to know, or do anything, just show me what I gotta change it it does this". "Buy the way, when do i get a raise".

Sorry man I got off a little bit. I really believe most people are good and have a good heart, just given some wrong directions sometimes, and the world just keeps dumbing things down to make it easier to just stay dumb I just sometimes worry about the next generation of customers expectations of quality.

[Small Tech]

I was working on a Trane gas furnace. As soon as the burners ignite they come on and off very rapidly. Here’s the sequence: the inducer starts, the HSI glows, and the gas valve opens and then the burners ignite and they sputter on and off very quickly sometimes they catch and sometimes they don’t. The blower isn’t running at the time this is happening and I did inspect the heat exchanger and couldn’t find any cracks. What would cause the flames to sputter very rapidly? Thanks for the help

is a s9v*? is this a convertible? They're missing caps on the inducer or they didn't properly connect the hoses during install.

I love trane, a life goal is to be a regional FSR. What model?

[cp3]

I checked the gas pressures and the voltage at the gas valve. I didn’t know what else it could be. I never ran into a problem like this before. That’s why came on here to see what else would cause the sputtering

[theoldscroll]

Did you check the orifices? sometimes a white corrosion gets around the holes of the brass.

[cp3]

Yeah I pulled the burners and made sure they were clean

[cp3]

What about clogged exhaust and/or intake pipes? Would a clogged drain cause the sputtering?

[Sooty]

What about clogged exhaust and/or intake pipes? Would a clogged drain cause the sputtering?

Absolutely.

[pecmsg]

Sounds like a lot of guessing...…………

Have you called Tech Support?

[Small Tech]

Birds nest or an unlucky squirrel in the flue pipe maybe? what are your inducer amps and pressure looking like?, if u bypass the pressure switch manually after inducer spools in sequence, does it still flutter? (obviously dont let it run for long.)