Oil Burner Puffback Explosion FAQs

Cause & prevention of puffback explosions
Oil burner puffback health concerns
Smoke, Soot & Odor warnings
Wind-related puffback

Noises Warning of an Oil Burner Puffback Explosion

Tip: See these key diaganosis and repair articles along with their safety warnings

• OIL BURNER NOISE SMOKE ODORS - home
• OIL BURNER OPERATING TROUBLE 
• OIL BURNER SOOT & PUFFBACKS
• OIL BURNER TRANSFORMER

Noise like a loud BANG! when oil burner starts

I have a 2 year old Trianco, external combi boiler which keeps cutting out. When I reset it, it makes a loud noise on igniting. (Oct 23, 2012) Rab G

Reply:

Rab G:

Watch out: A loud noise like a BANG when the oil burner ignites is usually a sign that un-burned oil in the combustion chamber is being ignited at burner start-up. This is DANGEROUS and can damage the heating equipment, blow off a flue vent connector and as a "puffback" can blow soot throughout the building.

Usually the problem is sloppy oil burner shut-down, fixed by changing out the fuel unit (expensive) or by installing an oil delay valve or stop valve (discussed at InspectApedia.com - just try the search function).

Smoke or Smell Warning of a Puffback Explosion

Oil smell and smoke when heat goes on, I replaced some stuff, now what?

Mike,smoke and oil smell threw out my house every time my heat goes on everything seems to be running fine so today i replace both filters ,cleaned the nozzle, clean ducts above unit and it still happened. what's next? (Jan 25, 2014) Anonymous

Reply:

Anon you are describing a system not working safely and at risk of a messy or dangerous puff-back explosion. I can't say from just your note if the problem is a blocked flue, lack of combustion air, or a cleaning and adjustment problem.

But if it were my house and oil smell and smoke were being sent by my heater throughout my house I would TURN OFF THE SYSTEM IMMEDIATELY and would call my oil heat service company for emergency service.

The money you save by trying to fix the system yourself may be much less than the cost of re-painting the soot-covered house interior or repairing other damage.

Thick black smoke at oil burner chimney, what's wrong?

The oil boiler furnaces smokes thick black smoke at the chimney. Whats wrong ? Please help !

The burner was cleaned but the problem stayed? On 2016-05-24 by Francois

Reply by mod: the system needs service and repair, and is unsafe

Watch out: if smoke continues to come from the chimney when the oil burner is OFF then there is a chimney fire - get out of the house and call the fire department.

If when the boiler is OFF you stop seeing smoke, then you should leave it OFF and call for repair. The burner has not been properly cleaned and adjusted, or something failed after that work was done.

Smoke and fumes 10 feet into the air over our chimney

My Super, Last Summer, Fired Up The Boiler, My Sisters Apartment is on the 5 th floor, She Has Holes in Her Ceiling, The Entire Apartment,was Filled with Boiler Fumes,

Now, The Fumes shoot out of the chimney, before this genius,the fumes were 1 ft above the chimney, now they re 10 feet in the air,

Did something go on the 5 th floor as far as the chimney,a plate or something else? On 2017-04-08 by john niemela

by (mod) - If a heating system chimney is leaking

John

If a heating system chimney is leaking anything - including exhaust or fumes - into the building, the chimney and heating system are unsafe, risking fire and (particularly when gas fired equipment is being vented into a flue) fatal carbon monoxide poisoning.

Watch out: I can't diagnose your situation by e-text but from what you describe there are serious, possibly fatal safety hazards in the building - the management, occupants, etc. need to know that immediately.

Oil Burner Puffbacks in Windy Conditions

We Get Oil burner puffbacks on cold windy nights

I get puff-backs on very cold windy day/nights, I think Root Cause is from poor design chimney that allows down draft(short, boiler in basement).

I have the same issue with when starting cold fireplace on 1st floor that is in same masonry chimney structure.

I put a small portable heater next to boiler aluminum flue air inlet before entering masonry chimney and it seem to resolve problem after I hear the first explosion. Suggest anything different. Very helpful site on all aspects of boiler service (Feb 1, 2014) Tom

Reply:

Tom, I think it might be smart to get a certified chimney sweep to inspect and advise about the flues; puffbacks can get worse and serious, even dangerous;

Watch out: We don't know if it's something as simple as a missing chimney cap or more dangerous, a blocked flue, damaged flue, or bad chimney design.

Or you could be lucky and just need a different chimney cap; some diagnosis of the actual chimney problem is needed.

Relating Oil Burner Soot to Puffbacks

Where does oil burner soot go and does it cause a puffback?

We had a puffback recently in our home and the mess was unbelieveable. We have our furnace serviced twice a year, but obviously something wasn't done correctly.

I have a general question - for an oil furnace, where does the residual soot go - up the chimney?

If the chimney is not maintained, then I am guessing the soot will build up in the chimney and then eventually back down into the furnace. Can this cause a puffback as well? I am new at this stuff, so your help is much appreciated. Your site has been very informative! - Lori

Reply:

Lori

Soot particles produced by fossil fuel combustion end up either deposited in the heating appliance or in the chimney except for those that manage to escape into the air along with flue gases discharged to the outdoors.

Part of proper oil fired heating appliance service includes cleaning and adjustment to keep the soot production low without setting combustion temperatures so high that while there is still less soot too much of your oil fuel dollar goes up the chimney.

Annual cleaning and service are very important for all heating appliances but particularly so for oil fired heaters since some soot deposition during the heating season is normal.

A puffback itself may be indirectly caused by soot accumulation if that accumulation prevents proper combustion or prevents proper operation of the oil burner.

But the immediate cause is the ignition of incompletely-burned or un-burned oil in the combustion chamber - an event that certainly has other causes (such as air leaks in the oil piping or any oil burner operating problem that prevents complete combusion).

Oil Burner Puffback Health Hazards

Tip: Details of the health concerns for breathing soot are at SOOT HAZARDS in BUILDINGS 

is a puffback dangerous to your health?

We had a puffback in our home is this dangerous to our health? Ins. co being notified. (Mar 17, 2015) Joan Thorson

Reply: yes possibly: the dose makes the poison

Joan it's a fair question to ask but not one that can be assessed by an e-text.

Watch out: Sure, breathing oil burner soot is potentially hazardous - it depends on the dose and exposure duration as well as individual health and vulnerability.

If you or any occupants have reason to feel concerned I'd check with the family doctor first.

The risk of breathing soot or other airborne contaminants has been well studied. A general remark I can offer is that the risk varies among individuals depending on a person's underlying health, age, other medical conditions, and of course the exposure level and duration.

Also see HEATING OIL EXPOSURE HAZARDS, LIMITS

and see SOOT on OIL FIRED HEATING EQUIPMENT

And of course any explosion can be quite dangerous.

Neighbor's chimney spewing soot, ash, smoke - is this a health issue?

My neighbors chimney spewed ash all over our yard and house and cars. They heat with oil and yesterday a new furnace was put in. However I want to know if the stuff from their chimney is a health issue for us and our pets? It is all over our dog and covers the entire block in our area. thanks, Peggy On 2018-01-11 by Peggy

by (mod) - Oil burner puffbacks can be dangerous

Peggy

Your neighbor's oil burner is or was not working properly and was probably unsafe.

The chief material in black ash from an oil burner is soot.

That can be hazardous, DEPENDING on the duration and level of actual exposure. That's not something one can assess by e-text. But you will read in the research I'll cite below that principal hazards are from acute exposure such as that experienced by oil burner service technicians.

See our research on oil burner puffback hazards

at OIL BURNER SOOT & PUFFBACKS

Oil Burner Puffback After Oil Tank Fill-up

Tip: Watch out: if your oil fired heating system ran out of oil it's likely that there is air in the oil lines. Just getting an oil delivery won't fix this problem. It's necessary to bleed air out of the oil supply lines before re-starting the oil burner.

If air isn't removed and you keep trying to restart the oil burner, un-burned oil may accumulate in the combustion chamber, leading to a puffback explosion.

Details are at OIL BURNER FUEL UNIT AIR BLEED PROCEDURE 

Oil tank fill-up overflow, then our oil burner stopped, then we had a puffback explosion!

I had my oil furnace cleaned three weeks ago and about a week latter the oil deliver man came to deliver oil and overflow the oil tanks causing a leak on the floor.

He went to the furnace and opened it to removed some of the oil to prevent the continuous oil leak from the oil tank cap. While he was removing the oil he kept on pressing on the ignition starter to force the furnace to run in order for him to remove the oil faster.

Couple days latter the temperature in the house dropped from 70 to 58 degrees.

I called the maintenance company that cleaned my system and when he turned on the furnace a puffback explosion occurred. What caused the puffback explosion in this case? On 2020-12-20 by Ali

by (mod) - oil burner puffback after oil tank over-filled

Ali

I'm sure sorry that you had a puffback explosion and hope the the first priority - making the heating system safe and functional - has been addressed.

The causes and underlying explanation of puffback explosion are given on the page above.

I'm unclear about exactly what your oil delivery person did nor how excess oil was removed.

There are certainly possible mistakes, such as leaving an air leak in the oil line, that could result in a later puffback explosion.

But when a puffback explosion occurs the first time a boiler is turned back on immediately after service and cleaning, then the problem is most-likely due to the service and cleaning procedure that were just performed, less directly than something that was done days earlier and considering that the heater ran through multiple heat-on cycles after that event.

By "less directly" I mean that if the oil delivery guy left the system not working properly that could have led to incomplete combustion of oil, accumulation of sludge and crud on the oil burner nozzle, loss of heat, and a subsequent need for a no-heat service call.

An experienced service tech might remember (or might forget) to check the combustion chamber for an accumulation of un-burned oil before turning the system back on.

Oil burner sprayed fuel into the combustion chamber which is sitting in a puddle

My boiler had a few false starts, and I guess it sprayed fuel into the combustion chamber which is sitting in a puddle. I replaced the electrodes and the nozzle and fuel filter, and it started right up and sounds smooth and quiet- but it is spewing out black smoke, so I shut it off. My question is, will the fuel oil evaporate or should I do something else? On 2020-04-19 by Ian

Reply by (mod) -

Ian

Lest you feel bad about the problem that you were describing, i admit I've certainly done the same thing and had the same problem.

You did the right thing to turn off the heater. The real risk is a dangerous and terribly messy puff back explosion into the building rather than just black smoke going up the chimney.

You need to be confident. The problem is just some temporary spillage and not something worse like a leak in the oil line connections or nozzle adapter that is continually spraying unburnt oil into the combustion chamber.

If you're confident that there's no actual leak and that there was a single event then what a service tech would do would be probably to pull the burner and wipe out any pooled oil to get things as clean and dry as possible.

She might then wait some hours before turning the system back on. At that point there will be some smokey exhaust but it should clear up in a minute or two. If it continues Beyond a couple of minutes I would be concerned particularly if the smoke was not diminishing and at that point I'm afraid I would have to turn the system off again for more cleaning and inspection for leaks.

by Anonymous

danjoe, thanks for setting me straight on this, while I thought that was the next logical step, I appreciate your explanation-
I'll do this tomorrow after work and report back in. Thanks

Reply by (mod) -

Stay safe and do ket me know what happens.

You shoul know that while you can get the burner to run, is not possible to properly set up and tune a modern oil burner without measuring smoke, co2, temperature, draft.

What To Do if the Oil Heater is Smoking

Tip: Watch out: If you see heavy black smoke coming from your oil burner chimney or if you hear a roaring noise at any chimney there may be a very dangerous chimney fire in process. In that case, get people out of the building and call your fire department.

Watch out: if your oil burner is smoking the system is not operating properly and may be unsafe. Shut the system off and call your heating service company for repair.

Watch out: if your chimney is smoking the same concerns as stated above also apply.

Help with an oil-flooded water heater that caught fire

I have a oil fed hot water heater, the primary ignition relay malfunctioned , causing the hot water heater to have excessive amount of fuel inside furnace chamber.

I cleaned as much of it. replaced the primary ignition ,When restarted the hot water heater spews dark gray smoke from chimney, also noticed when I shut hot water heater off,

I ck'd access hole to furnace(hot water) there was a fire inside. I put out fire with water. I need help - Matt

Reply: flooding the water heater ignited unburned heating oil and risked a "puffback" - clean or R&R oil-soaked combustion chambers before re-igniting the burner

Matt, fresh out of oil burner school we were always terrified about lighting off an oil burner into a previously flooded combustion chamber and flat wouldn't do it if we hadn't cleaned the system and even removed/replaced oil-soaked combustion chamber liners.

And if the chimney was of unknown condition we'd have it inspected (Chimscan, the works) - even so, it was not unusual to call the fire department and have them on stand-by: that's what we were taught to do.

The first time I called the fire department to ask them to go on stand by while we fired up the boiler, the fire department operator said "maybe you should get someone in there who knows what they're doing" - which didn't inspire much confidence.

Now that you've had a fire you really cannot safely turn the equipment back on before an expert inspects the chimney and flue for safety;

A modest oil residue in the combustion chamber can be burned off. But a really flooded chamber deserved to be disassembled and cleaned or replaced.

Oil Burner Soot blamed on power vent and chimney, reappears after clean-up

I had a problem this past spring with black soot throughout my home. We had 2 different companies plus a mechanical engineer come in to determine that the furnace was fine and that the cause of the black soot in the house was from the power vent.

We got the house cleaned by a fire cleanup services company and all the rooms were painted because they couldn't get the soot all out. We replaced the power vent with a chimney.

I am beside myself that I have again found the black soot coating white plastic containers in my kitchen cupboards. I have contacted a materials lab and was told that I would need a good amount of the soot in order for them to test it. This could take a very long time to collect because it's a black film that smears.

I don't know what else to do or who to turn to for help. I can't go through what we did this past spring. Do you have any thoughts and or recommendations as to what I can do? Thank you for your time! (Dec 5, 2014) Amy

Reply:

Sorry to read about this soot Amy - perhaps the original diagnosis was erroneous. After all, a sooting-up oil fired heating system can clog a power vent just as it can clog a flue vent connector, heat exchanger, or chimney.

You need help from a trained and experienced heating service tech.

Let me know what you're told.

How do we fix an oil furnace that is smoking?

Montgomery ward 700 oil furnace.
Started smoking up vents after it shuts off.
Chimney is clean.
How to clean it. Model mp98 On 2020-09-17 by Priscilla Riddle

Reply by (mod) -

Priscilla

When you get smoky flame at shut down on an oil burner then the most-likely cause is the oil burner's fuel unit our pump's shut down valve is dirty, clogging, not working properly.

That's an internal valve in the pump that's designed to stop the oil flow quickly when the motor stops turning. If it doesn't work then low pressure oil is sent through the nozzle where it burns incompletely, hence the smoke.

Watch out: The risk is a dangerous puffback explosion.

That shutoff valve is not usually serviced in the field but rather the service tech will replace the fuel unit itself.

Don't try it yourself.

Oil Burner Puffback Causes

Tip: See these key diagnosis and repair articles to prevent an oil burner puffback

• OIL BURNER NOISE SMOKE ODORS - home
• OIL BURNER OPERATING TROUBLE 
• OIL BURNER SOOT & PUFFBACKS
• OIL BURNER TRANSFORMER

What caused rumbling chimney and black smoke and soot from our oil boiler?

What causes water sound in my vent and black smoke came out of the vent once. There is a boiler system here. On 2018-01-22 by Kelly Mingus

Reply by (mod) -

Kelly

You may be hearing the sudden ignition or 'explosion' of un-burned oil that collects in the combustion chamber if an oil burner is not working properly.

Watch out: such explosions can be dangerous as well as making a sooty mess of a building. Ask your heating service company to inspect and repair or adjust the system.

Do "faulty boilers" cause puffbacks? Where do I look for puffback damage to the boiler itself?

Thank you for your informative website. As a homeowner trying to deal with a puffback it is a sight for *dirty* eyes!! Under the heading
What Causes Sooty Puffbacks at Oil-Fired Heating Boilers, Furnaces, Water Heaters [article above] there is a statement in paragraph one that states "Depending on the quantity of oil that is ignited, the puffback can damage the boiler itself...".

This seems to be the opposite of what my insurance carrier is telling me. They maintain that a faulty boiler causes a puffback and thus is not covered under the homeowners policy because it is the culprit, only the damage it causes is.

Where would I look to determine what, if any, amount of unburned oil could have actually damaged my boiler? Thanks, D.F.

Moderator Reply

Our InspectAPedia photo (above left) shows soot on the ceiling of a garage just outside a boiler room where an oil-fired heating boiler was operating improperly and blowing soot into the building - a puffback from this system was imminent.

This is not the building discussed by D.F. above. As you can see by the exposed wall studs in the right side of the photo, we had already begun demolishing the sooty drywall in this home.

Reader Follow-up:

Thank you so much for your answer. I have since learned a bit more about boilers and would like to correct some confusion with my wording now. I do apologize as boiler jargon is really not my thing. My boiler has been maintained but it is aged.

I had shut down the system for the season, or so I thought. It was an unusual damp, wet May. I suspect one of the kids hit the on switch at the entry to the basement.

Regardless, since the boiler has to be replaced I am trying to learn. I am trying to understand the term *inherent vices* of a boiler that exclude replacement coverage under the homeowners policy.

I am coming to understand that there are some condition that are known to cause the boiler to "damage itself". In other words, wear and tear, causing a puffback.

However, the wording in your article led me to question whether the oil/puffback could be an "external" element that caused the damage to the boiler. Its sorta like what came first, the chicken or the egg. There were no visible leaks so I am wondering how the "excess oil" could have gotten there.

Are there any possibilities that tie in the oil tank (outside underground)? Either way, I am learning it is an uphill battle to actually get the boiler replacement cost covered which; is a real expensive bummer. After all, protecting against a big expense like this is why you buy insurance in the first place.

Reply: Do faulty boilers cause puffbacks? No, oil burner problems, oil piping leaks, or chimney maintenance troubles are the root cause of puffbacks.

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem with or cause of malfunction in a heating boiler. That said, here are some things to consider:

Your quotation from your insurance company stating that the puffback was caused by a "defective heating boiler" is confusing because it is not a precisely correct description of heating equipment puffback problems.

The explanation we offer of the mechanism of a puffback in oil fired heating equipment is more detailed than a typical insurance adjuster would offer even if s/he understood the cause of puffbacks, but our explanation is also the correct one.

Our photo (above left) shows soot fragments on top of a water heater that was installed close to an oil-fired heating boiler that was not operating properly - the same boiler whose soot was deposited on the garage ceiling and walls in our earlier photo just above.

Failure to notice and do something about this sooty boiler operation is a failure to notice and correct a boiler operation or maintenance problem.

After combustion air "adjustment" our boiler had a big blowback explosion

My old Trianco boiler was seviced this week and the engineer changed the air flow incorrectly causing bad misfire. Came back to change settings back to what is was previously but still did not solve problem.

Then third visit by a supposedly more experience engineer. Seemed to be running weel when he was here. Following day boiler did not fire up on start (reset light on).

On nexr start up attemp there was a big blowback blowing the flue off the the top of the boiler and the top off the chimney! Obviously not happy at all but where do I go now?

This is obviously going to cost me big to repair the chimney and flue even if the boiler is still alive! Any suggestions as I'm sure I want these guys any where near my place after this! On 2017-09-24 by Nigel

by (mod) - more causes of oil burner puffbacks

Nigel,

There are a number of problems that can cause the puff back malfunction that you described. I can't list them all off the cuff and besides your on-site expert needs to look and find the actual problem.

Examples however include insufficient combustion air into the space where the burner is operating, or even a leaky or incorrectly installed or incorrectly selected oil burner nozzle or nozzle adapter.

Even a small air leak in the oil line can cause the problem that you described. So can I block chimney or flu.

So Further investigation by an experienced service technician is needed to check out the basic metrics such as combustion air, flame pattern, draft, in order to get an idea of the direction to look for the problem. Let me know what you're told and I can come in further.

What's the cause​ of oil burner catching on fire?

What's the cause​ of oil burner getting on fire. Dark some from the chimney, co2 inside if house...High levels. After the cleanup and service been performed..Still can smell burning oil...that's 3 days later.(Apr 3, 2017) Maria

Reply:

Maria

I'm not sure if you are asking about a fire at the oil burner or a chimney fire.

Watch out: But it sounds as if your heating system is unsafe and should be turned off immediately,

then call your heating company, speak to the service manager, tell her that your system was just serviced but that now it is smoking, not working, and had to be shut down to avoid risking a puffback explosion.

Olsen furnace ran for about 30 seconds while smoke emanated from the ductwork going into furnace

We have an Olsen oil furnace that is not firing when we turn up the thermostat. went down to the furnace, and pressed the red reset button once on the beckett motor. it ran for about 30 seconds while smoke emanated from the ductwork going into furnace. quickly filled crawlspace with smoke.

shut off the burner switch and put the thermostat at 0. any thoughts on whats going on? (Oct 14, 2017) Nick said:

Reply: it ran for about 30 seconds while smoke emanated from the ductwork going into furnace

Gary and Nick:

Watch out: LEAVE THE BOILER OFF right away to avoid a puffback explosion.

Most-likely the automatic oil line shutoff valve/check valve in your fuel unit (oil burner pump) is sticking open. Sometimes we make a temp fix by adding an oil delay/stop valve on the line between the fuel unit and the burner nozzle oil line inlet.