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Problem with \"Flashback\"

of a Utica DV50BLP boiler, power vented. After running for a few minutes the gas flame will flashback in the burner, burning at the orifice. There is no air shutter on this burner. If I shut if off and restart it will be fine for as long as 10 to 15 minutes then it flashs back again.

I have the LP gas pressure set at 10.0" W.C. with a 47 drill size orifice, single burner 50,000 BTU's. Specific gravity 1.52 BTU content 2550 BTU's per cubic foot.

This is a side wall vented unit air for combustion from within the building and there is plenty of air as this is a big wide open garage area.

Combustion analysis CO2 9.5%, O2 4.8%, Flue gas temp 250 degrees CO 25 PPM air free.

I have tried everything to solve this problem nothing works. Any ideas?


  • D luxD lux Member Posts: 230
    are the burners level ?

    I cant rember if nat gas can be slighty uphill and lp down hill or the other way around
  • S DavisS Davis Member Posts: 491
    Manifold Pressure

    What is your manifold pressure, the 10" is that at the gas valve inlet?

    S Davis

    Apex Radiant Heating
  • This boiler has

    a single burner and it is fixed in position when in place and has no adjustment.
  • The pressure

    at the inlet is 11" W.C. and at the outlet it is 10" W.C. I tried boosting the outlet pressure slightly but my CO reading started going up.
  • S DavisS Davis Member Posts: 491
    Gas Pressure

    It sounds like low gas pressure to me, have you checked the burner orifice for earwigs or other bugs they love propane.

    S Davis

    Apex Radiant Heating
  • hrhr Member Posts: 6,106
    Years ago

    I had this exact problem with another brand. Finally after many adjustments and plenty of hair pulling, the factory had us space the burner tube away from the orfice with some flat washers. Merely increasing the gap between the end of the orfice and the burner tube opening. It worked!

    hot rod

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  • SteamheadSteamhead Member Posts: 11,373
    \"Garage area\"

    Is it possible some flammable vapors are getting into the combustion air intake duct?

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    Baltimore, MD (USA) and consulting anywhere.
  • Frank, This is a brand new

    building there is nothing in the building at this time. It is too bad because when it is running the radiant job we put in is working like a charm. It is the boiler giving me a problem. Should be a cup of tea for me as I have tackled this many times in my career and a minor adjustment to the air shutter usually solved the problem. This boiler does not have an air shutter. I actually made one just to try it and it still flashback. I am, getting to old for these headaches.
  • Thanks Hot Rod,

    I think Utica anticipates this problem as they allow movement of the burner back and forth about 1/2" or so. I have had this sucker in every position imaginable and it still is givng me trouble. I am going to contact Utica Monday to see if they have any ideas. The last Utica I had a problem with brand new we finally replaced all the burners and it solved an excessive CO issue. I really am begining to think it is a defective burner, I just can't see anything wrong with the burner visually. When the flame is on the burner it looks good and I get get good combustion readings.
  • Jim Davis if you are

    not to full of turkey your buddy Tim could use a hand. Give me a call 401-437-0557 or go ahead and post something here.
  • SteamheadSteamhead Member Posts: 11,373
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • That is my feeling

    Steamhead, I am going to see if I can pick up a new burner Monday. There is something else that I have been seeing on gas burners lately. It is a small hole drilled just after the primary air opening on the top of the burner. I do not know what it is for. I tried covering it over to see if it affected burner operation it did not change things.
  • Bob HarperBob Harper Member Posts: 732
    deja' vue?

    Isn't that sorta what a flashback is? Oh, wrong kinda flashback...
    Tim, since you cannot adjust primary aeration, the other variables I see are: manifold pressure, burner design, burner port loading, alignment of burner orifice spud into the mixer tube and the proximity of the venturi to the burner. We have some fireplaces that are prone to crossover ignition when the pilot is close the the venturi. The was corrected by installing a shield btw the two then redesigning to burner with a lower port loading. The porting has a lot to do with it. Some units, the ports are too big while in others it happens in coalesced flames. In some units, we've had to make a vena contracta in the mixer tube immediately downstream of the orifice.

    Can you check that burner for cracks? Since you say this manifests after it has been firing awhile and not at cold ignition, this could point to a crack that opens as it gets hot. When you look at a chart for LP burner design in the Gas Engineers Handbook, it shows the curve for flashback primarily at low manifold pressure over a fairly wide primary aeration. Since port loading drops off as the burner heats up, maybe this in conjunction with a crack are the cuprits.
    If I think of anything else, I'll holler.

    Man, I'm O.D'd on turkey...
  • Thanks Bob,

    I have considered some of those things. I observed that on this pressed metal burner with very close port loading that some of the ports are wider open than others. I have spent some time going over the burner with a mirror while it was firing can't see any visible cracks.

    I even tried boosting the pressure up to 11" W.C. I have just about exhausted all of my 40 years experience on this one. Thanks for your help everyone, keep it coming as I am going to go back Monday and retry everything. I have to be missing something. For my students when I talk about finding problems in 20 minutes or less this is the other one I mention that takes a lot longer than 20 minutes to find.
  • Mark EathertonMark Eatherton Member Posts: 2,542
    Burners suck...

    air into their primary port due in part to the secondary air going through the combustion chamber. I've gone as far as putting my hundredths of an inch manomoeter into the primary air input to see what kind of vacuum is being maintained. You may need to do that too.

    Seems strange though that it happens AFTER the burner has been running for a while. Can't hurt to check it though. I've seen as high as .10" WC negative in the throat of the burner.

    I've also seen cases where the secondary air screen that fits around the primary side of the burner had come loose, thereby negating the induction action for the burner, thereby causing flash back.

    I have no doubt in my mind that you will get it resolved...


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  • WeezboWeezbo Member Posts: 6,232
    two three things come to mind....

    propane will cool down real rapidly on a call for use when the regulator is undersized...then there is another thing the regulator can be faulty from the gate...meaning you think it is new and it is indeed vintage...and something that has jack to do with the regulator or pipe size, actual available air. really though, it sounds like the regulator on the tank.
  • TonyTony Member Posts: 608
    That hole

    Can have a sheet metal screw inserted into it. It will act as a kind of "throttle" to slow down and spread the flow of the gas/air mixture. Just start the screw in and adjust in or out until you get the flame you want. Works like the old Armstrong burners from the 70's. Personally, I believe you have a burner that isn't up to snuff.
  • DavidDavid Member Posts: 250
    I saw same problem

    on a Utica boiler, but not as often. Problem was solved by replacing the regulator at the tank. I believe Utica wanted 14" supplied to the boiler.

  • MIKEMIKE Member Posts: 99
    Utica problem

    Utica boilers are very common around here.They are known for this flame in the venturi problem and pilot outage problems.The last time we had a problem with a nat gas burning in the venturi we were given burners with adjustable air shutters instead of the factory set ones.The factory reps there are not very helpful,you know more than them,so do I for that matter.BTW you had a problem with two similar boilers in the same basment one worked and vented fine and the other was a problem high co i think what was the out come
  • tim smithtim smith Member Posts: 2,226
    Burning back in venturi

    I am thinking that it may be the type of orifice, I have heard that based upon the type, it will entrain air differently depending on the type not just the size. good luck, Tim
  • What they called

    a breaker bolt which when screwed in and out controlled gas flow which affected primary air intake. there is nothing in the manufacturers instructions to indicate that is what it is for. I will hopefully find out tomorrow if that is what it is for when I call Utica.
  • Problem with demand

    for pressures greater than 11" W.C. from Rego and Fisher and other LP second stage regulators is that it violates recommended protocall on their regulators. All the charts and graphs for those regulators set up a maximum 11" W.C. outlet pressure using proper pipe sizing to accomplish proper delivery pressure not increased regulator pressure. If Utica give me this as a solution it will have to be put in writing on formal letter from thier engineering department. If that is what this new equipment is getting to with demand for inlet pressure higher than normally provided then we need to have some drastic changes made in the natural gas and LP gas industry.
  • Mike we solved that old Utica

    problem. I have been waiting to post some info on what we did and am going to be doing a full analysis with a class I am running on December 7 on Combustion Testing so I will get back to you on that one. In the meantime thanks for the info.
  • Tim I converted this

    with the orifice kit sent by Utica to convert from Natural gas to LP so I would assume it is the correct orifice. I may have to before I am done look to a different orifice.
    I just hate to start having to fix equipment that is brand new. I do not mind making adjustments and doing fine tuning that is our job in the field. This is beyond fine tuning and adjustments. It does point out what Jim Davis and I talk about all the time and that is just because it is new does not make it okay. I never trust anything new I have to always test everything twice.
  • I have taken that orifice

    out and cleaned and looked at it so many times I am seeing it in my sleep. The next thing I looked for was a spider web up inside the manifold no such luck that would have been to easy.
  • Thanks to everyone

    for all your input it helps tremendously as it makes me check myself. I will try some of the things mentioned if I do not get action from Utica. I will let you all know how I make out.
  • curiousity killscuriousity kills Member Posts: 118

    Tim it sounds by your readings like the system is slightly underfired?Flue temp seems low and o2 seems a little low.I know you said it was powervented but what as draft?Typically see a 7 to 9 o2 on gas.Possible low draft?Possibly underfired?Good luck
  • WeezboWeezbo Member Posts: 6,232
    Tim ,in a recent super troubleshooting nat gas class i asked

    the tech rep about conversion to propane from nat gas on a burner the tech said there is a screw that adjusts for flow to get the correct burn on the gas valve he said that on nat gas you dont adjust it at all on propane you adjust it according to the orifice you are, that sounds like maybe the trick to that as you mentioned something similar in the post above...even though i read what you are experiencing it still sounds like the regulator to me.
  • Quick answer from Utica

    they are sending a dedicated LP burner to try as a possible solution to this problem. Another possibility is a manifold out of alignment. The burner is coming next day air and we will be checking a few more things today. We should have this licked by Wednesday. I will keep you posted.

    Thanks to Pete Desens from Utica for his quick response and great attitude concerning this problem. also to "Joe" at Utica tech center for his response to my sons call and suggestions for solutions.

    Let us hope this will solve the problem. I might just have the LP company change the regulator to be safe, I will have to think about that.
  • DaleDale Member Posts: 1,317

    Had a heil that had the one burner problem, manifold wasn't tapped correctly for that orifice. Manifold out to water hose should have all squirting the same plane. Adjustable burner will probably fix the problem but is the LP tank full? Has anyone put a gauge at the inlet to the LP reg at the house and compared it to the tank outlet? Also, going up and down a few drill sizes on the problem burner may be worth a try, your flame speed is too close to your flow velocity so maybe a mix of things. Also, have you pulled the sheet metal away from the top of the boiler to see if there's any slight difference in the casting spacing of flue collector area? Anxious to hear what you find, good luck
  • PlumdogPlumdog Member Posts: 18
    Orifice Size

    Sometimes when derating for altitude (over 10,000 ft on occasion, and frequently at 8000 ft) we get one or more burners that the flame will jump back to the orifice and create a noisy whistle or the noise can start without the flame jumping back. It usually is solved by smaller drill size and more air. Some of the reps say you don't have to derate for altitude, but we find that to be untrue. Nat. gas is already diluted to a lower btu content when delivered at higher altitudes but the same is not true for LP gas.
  • DavidDavid Member Posts: 250
    Any news today? 11/30

  • David and others

    the new burner came by next day air today from Utica. I will be installing it tomorrow and will let you all know how I made out.
  • New burner installed

    and everything is working fine. The burner is dedicated for LP gas and has an air shutter, by the way that is what the small hole in the burner is for to hold the screw that secures the air shutter. The burner has less slots cut in it than the other burner which was for natural gas, for better port loading and it fires nice and smooth with no flashback or extinction pop. I left the air shutter wide open as the CO started to rise when I closed it up.

    I could not do a combustion analysis today as someone was using my tester on another job. I did however do some tests with another type tester I have. The flue gas temp after the power venter is now 325 degrees net. The CO remains at 30 PPM. I am going to go back and adjust the pilot with my microamp meter and do a final tune up with combustion tester.

    Thanks to all of you who offered assistance it really helped.
  • DavidDavid Member Posts: 250
    Thanks for update

  • WeezboWeezbo Member Posts: 6,232
    Are there any other \"designe details\" that were\" other\"?

    Is there some indication in the fine print from the manufacturing Team that You were Supposed to Know ? These minor technicalities should not be in our trade really,or is the ommitance of some detail to "Throw "the installer just for devil of it, you know, just to keep him on his toes as he wastes days of his life remanufacturing every last element on or adjacent to the product that may or may not have some concievable no matter how remote connection to the abberance...? this is where manufacturers could really help out... Tim ,I think ,you were lucky that your not in and out and gone,you had the chance to live there with it now for what seems a week! Most installers dont really have quite that luxury.....
  • Weezbo in all fairness

    to Utica and others this is an unusual problem. I have converted many boilers and furnaces over the years and did not have any problem with combustion issues. It has usually been the case that one burner fits all. I am blessed to have years of accumulated knowledge to draw on in these situations. Every once in a while I run into one that is not easily solvable. There is as I teach my students always a solution. You just have to search it out sometimes. I am so glad to now have this venue (the Wall) to sound out my difficulties and get such wonderful help.

    I do agree with you that it would help if instructions were made avilable that told us what a combustion analysis readout should be on equipment and in addition possible problems that may be faced when converting from one gas to another.

    I really did not spend that much time on this I would say about a total of four hours not including travel time.

    It is also my opinion that I tend to do a lot of things when setting up equipment that others may not necessarily take time to do. I have even been know to polish the gas lines and emory cloth all the copper fittings and pipe.
  • I should also thank Jim Davis

    for calling me the other night. It is so good to have someone who is on the same page with solutions to these problems and Jim gave me some definite confirmation of my suspicions on this one.

    I am used to having others around to sound of my problems on. When I was with the Gas Company there were a hundred other service personnel to get opinions from. I miss that sometimes but then I come to the Wall and there are all these great inputs from all who dwell here.
  • WeezboWeezbo Member Posts: 6,232
    *~/:) Ehhh I like 4 0000 steel wool myself :)

    it actually poishes the copper and brass till it shines ,Then ...If You Shoot Hot ,Really Hot water through it , it gets a niceGold Glow to it ,and that remains for decades :) cool ? *~/:) My buddy Fred ,He likes 1 0 it is more agressive ....
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