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GB 142 lockout due to Hoar Frost (ME)

Exhaust points straight up, and C/A has a 180 degree elbow with 2' of separation betwixt the two. No chance of exhaust gas recycling here.



  • Any one else experience this?

    Before I begin, I should point out that this post is NOT intended as a criticism of the boiler manufacturer, and that I have had this problem with other sealed combustion appliances. Unlike certain people who recently started posting here, I don't beilive in public floggings as it pertains to individual appliance manufacturers. The premise of the sqeuaky wheel getting the grease sometimes doesn't work. The premise of honey catching more flies than vineager does... But I digress.

    Got called out to a job with a GB142 Friday night because of an A 6 lockout, which is not in the manual, but was told by the local rep it has to do with 3 trys for ignition and no flame. When I get there, I suspect a problem with gas pressure, so I check the incoming gas pressure and find it to be rock steady. When I first pulled the cover off the boiler, there was a slight odor of natural gas. Leak checked gas train and found no leaks.

    Test fired unit 2 dozen times, and never missed a beat. Turned off gas supply and confirmed lockout code. Reset, and unit took off fine after I turned on the gas. Tried shutting unit off 12 times in mid cycle at gas cock and got no error code, just retry's for iginition.

    On my way up there, I noticed that the pine trees were stunningly beautiful due to Hoar Frost...and the fog was so thick that you could not see more than 50 yards away.

    Put the unit back together again.

    Got a call the next morning that the unit had locked out again. Had the customer reset the boiler and retry for ignition. Said it went immediately into lock out three times and shut down. Had him pull the jacket/cover off the boiler, and reset and unit took right off, no problem. Have not heard from him since.

    I suspect that the combustion air inlet screen became completely blocked due to Hoar Frost and the cabinet cover fits so tightly on the appliance that it was starved for combustion air, and could not light, and consequently locked out.

    My possible solutions are as follows.

    Cut a barometric damper into the side wall of the cabinet, thereby giving indoor combustion air a path should the OSA path become blocked, OR...

    Install heat tape around the annulus of the combustion air intake pipe and wire it in parallel to the boiler pump. If the pump is on, so is the heat tape.

    On other systems, on the same ranch where I experienced the same frost/blockage situation, I disconnected the combustion air pipes, and left them that way, and the problem went away. And I could easily do that in this case, but its obviously not the "right" fix.

    Anyone else experience this condition?

    I would imagine that the CO was probably off the charts due to "choking" syndrome occuring at the gas valve near total frost blockage. Good thing its a sealed combustion unit...

  • Mitch_4
    Mitch_4 Member Posts: 955

    although not on that boiler..mstly FA systems here.. it was VERY common about 15 - 20 years ago when furnaces used screens..no one here uses them anymore and every manufacturers tech line I called said pull em. they dont stop bugs, and birds are too rare to warrant.

    pull it.

  • S Ebels
    S Ebels Member Posts: 2,322
    Lot's of times

    There are scads of 90% furnaces around here that are improperly done at the vent termination. This is usually the cause due to the fact that exhaust gases are recirc'd into the intake and the venturi effect being what it is, gradually seals the intake off with frost. Happens especially during the atmospheric conditions you mention ME. Still air, high humidity, cold. I'd wager we get at least a dozen or so calls each winter from this. Usually, reconfiguring the vent takes care of recurring problems. Inside corners of houses are especially bad, try to get the vent terminated on a nice long flat wall. RIIIIIGHT! Like they leave us space for that!

    I have to say that I have never had a concentric do this. Probably because the exhaust is blowing directly away from the intake. For non concentric applications, we bring the I/E pipes out of the structure within 6-8" of each other, turn the intake down with a 90, then bring the exhaust up 12" and terminate blowing stright out from the wall. Done like that, we usually don't have any problems. Some of the HO's complain about the exhaust plume but that's just a characteristic of a condensing appliance. Get used to it basically.

    On your situation Mark, how is the termination done? Roof? Sidewall? How far from a corner?
  • Jeff Lawrence_25
    Jeff Lawrence_25 Member Posts: 746
    Customer had a bird screen

    On their 92% furnace. Sure kept the birds out and gave the wasps a great, well protected place to build their nest. Furnace wouldn't fire off because the nest was so big.
  • rich pickering
    rich pickering Member Posts: 277

    Low fire can also be a problem, there may not be enough velocity to get the exhaust stream far enough away from the combustion air inlet. Concentric or 2 pipe, same problem.
  • ScottMP
    ScottMP Member Posts: 5,884

    I've seen it happen and I would change over to a concentric. I would guess that the intake travels thru a unheated space before it gets to the boiler ?

    If I was to put heat tape on it I would leave it on all the time. The Frostex style actually has a thermostat built in. Having it come on with the pump dos'nt allow enought time for it to warm up enough ( that stuff is pretty slow .

    By the way, what about insulating the intake ? I would think the cold air is freezing in the side if the pipe and building up.


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  • Scooter...

    I wish it were that easy. The roof is a metal ridge roof. We had to go with separate penetrations due to numerous reasons which should be obvious once you take a gander at the attached pictures.

    The only unheated portion of the pipe is that part that is outside of the mechancial room. See attached pics for splanation.

    Insulating the lines would have no effect because the hoar frost is building up in the inlet/throat on the outside of the combustion air inlet. The mechanical room, although not heated, has plenty of radiant energy from uninsulated piping within the room. It is NOT cold in the mechanical room because of the sealed combustion appliance.

    Thanks to everyone for their input.

  • Brian
    Brian Member Posts: 285

    > I wish it were that easy. The roof is a metal

    > ridge roof. We had to go with separate

    > penetrations due to numerous reasons which should

    > be obvious once you take a gander at the attached

    > pictures.


    > The only unheated portion of the

    > pipe is that part that is outside of the

    > mechancial room. See attached pics for

    > splanation.


    > Insulating the lines would have no

    > effect because the hoar frost is building up in

    > the inlet/throat on the outside of the combustion

    > air inlet. The mechanical room, although not

    > heated, has plenty of radiant energy from

    > uninsulated piping within the room. It is NOT

    > cold in the mechanical room because of the sealed

    > combustion appliance.


    > Thanks to everyone for

    > their input.


    > ME

  • Brian
    Brian Member Posts: 285

    I haven't had this problem with any of my GB's.But I used to get it with the Trinity s I installed.What about lengthening the exhaust about 12".Even though it's installed by instructions it would decrees chance of cross contamination.

    Good Luck
  • Brian...

    THere is three feet of separation between the two pipes. Manufacturer only requires 10". Exhaust gas recycling is not a problem.

    Owner had a wind study done in anticipation of possibly doing a wind farm, and prevailing breeze is exactly as you see it with the plume going up the roof.

    Cross contamination will not cause the lock out code that we kept getting.

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Yet another goofy idea...

    If you don't want to remove the inlet screen why not install something like a bell reducing coupling over the existing inlet?
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Thanks Mark for making me look up "hoar frost"!

    If I'm understanding correctly we had one here in Swampeast MO this morning. Conditions were perfect and there was a special weather statement warning motorists.

    Virtual snow on exposed surfaces and beautiful in the sun before it rapidly melted...
  • Brad White
    Brad White Member Posts: 2,398

    Just a wildcard thought, but ever see fog rise from snow? Thinking the evaporation from roof snow being sucked in, re-freezing from vapor state to rime ice.

    (I used to use your term but only to describe a chilly reception from my ex-wife) :)

    Anyway, having seen rime ice form on Mt. Washington out of fog, it resonates with me. Wondering if a taller inlet stack might make sense. Has this happened without snow present, just from ambient moisture?


    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • S Ebels
    S Ebels Member Posts: 2,322

    I've not installed a GB but nearly every manufacturer manual I've read indicates the exhaust must terminate at least 12" above the intake , be that hoarizontal (pun intended) or vertigo through a roof. Our roof penetrations are always done that way because I don't like getting up on snowy roofs in the winter. NOT FUN! Not saying you don't know what you're talking about mind you, I just find it interesting the Buderus doesn't call for that when darn near every manual that I can recollect, does.
  • Not sure Brad...

    We typically didn't get the call until the next day. Rarely is it extremely foggy up there for two or more days in a row. For some unknown reason, the frost only builds up on metal components, and there is a stainless steel vermin screen up inside of the return bend fitting. Rep said we should pull the screen because the only thing it really keeps out are small animals.

    Check out the sound this boiler is making when it approaches 180 degrees F. It has glycol in it. The residents wanted to know if there was an airplane in the mechanical room...

    Buderi engineers are working on it.

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    That's "just something it does"?!?!

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    I hate to say this but why does what looks like a new house need 180F supply temp with a boiler that's designed around a law-required maximum of 167F in its homeland?
  • DHW production...

    THe rest of the time its running in the condensing mode.

  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Seriously here...

    Are the homeowners setting back during the night to the point that the boiler rarely if ever runs and then expecting a rapid heat-up in the morning with emitters that can't deliver full boiler output?
  • Darrell
    Darrell Member Posts: 303

    Happens here alot, especially down in the river vally when its cold but the river is still open. Doesn't have to be the exhaust standing in the air...although that will cause it to happen too. It happens when saturated cold air is accelerated over or around an obstruction or anything that can cause turbulence like an elbow or screen. Hoar frost is the result. The best method we've dicovered for prevention is to take the exhaust out the roof through a large diameter concentric vent...six inch b-vent or so...the combustion air is drawn through the roof cap which has a large area and allows the air through without accelerating it too much. The exhaust is blown strait up where it can turn to frost or drift away without causing too much trouble. The more efficient the boiler...mod/con.. the worse the problem seems to be. If we take the exhaust out the side wall it'll lift the siding right off the sheeting. I've seen ceilings fall in when the spring thaws all the frost in the attic that came in through the vents. The newer boilers that do not give a roof penetration option are being a problem...I make alot of money clearing frost and resetting from lockup.
  • ScottMP
    ScottMP Member Posts: 5,884
    Thats a tough one Mark

    I am leaning towards eliminating the screen also. MY other thought was to lower the inlet but after this winter is pretty obvious why you need the hieght :)

    Funny with dry winter air you would think that contamination would be the culprit, it certainly was in my case. I suppose if its building up on that screen it just grows.


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  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    A concentric vent

    is not the solution. I've had wasp nests in the inlet air with them before. The problem with roof terminations is checking the inlet when you've just had 3 ft of snow. I'd sub out spider man for that job. :) I think the barometric damper's not a bad idea. WW

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  • Brad White
    Brad White Member Posts: 2,398
    Re-Evaporation [2]

    I think Darrell was honing in on what I was thinking, Mark, that the velocity in a moist environment speeds cooling by evaporation.

    The snow being the most likely source of moisture (it is frozen vapor not frozen water afterall) begs the question, does this happen when it is cold but no snow to be found? (I know, I know.... "no snow" is but a distant memory to you...)

    The screen has a free area that is considerably less than the whole opening, so velocity rises. Moisture evaporates and sub-cools below ambient at that point.

    Metal is more conductive hence more receptive to collecting the stuff. The plastic screen idea offered by Jeff Elston is on-track to my thinking but over-sized to thwart the velocity-based cooling.

    Rime ice forms on metal far more prevalently than wood, plastic, etc., to illustrate that point.

    Now, if you did pull the metal plate (don't tell the voles), what happens?

    Random thoughts from Back-East.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad

  • May not be related mark, but we're seeing condensation on the BURNERS of a few Ultras that are on very low firing (low temps, cycling below minimum). We suspect the burner isn't warm enough to heat up the leftover cold gas in the burner when it's done firing.

    This keeps the flame sensor from reading a flame, as the condensate pools under the burner, where the flame sensor is.

    We get lockouts from like this too. Any chance this is what's happening on the GB?
  • Darrell
    Darrell Member Posts: 303

    It can happen in clear air...no snow, no fog. At temps below zero the "dry air" outside can be nearly 100% saturated...ready to condense onto anything in the form of frost, and the acceleration over the intake drops the dew point just enough to cause it to do so. If there happens to be fog...the dew point has already been reached and frost is looking for a place to happen.

    With a roof penetration the warmth from the flue seems to keep the roof cap free of frost. Never had a problem when the vent is done this way.

    It also doesn't seem to make much difference whether the screen is metal or plastic...all the frost needs is turbulence.

    Another problem I see alot with the side wall concentric vents is frost getting sucked into the intake...shatters the HSI ignitor, or pools in the bottom of the boiler, cruds up the ignition and proving circuit. I've had to disassemble concentric sidewalls vents and chip the water ice out of it...those probably weren't installed the best...sidewall, alcove, lots of frost in the intake, then the frost melts at idle and pools freezing solid, even if the vent is pitched to drain.
  • S Ebels
    S Ebels Member Posts: 2,322

    That would definitely get a person's attention! Sounds like a seriously sick Lennox pulse furnace without a muffler. Or my diesel Super Duty when it's cold. I have to think that it has to be some sort of an intake harmonic or something that's causing the burner to not mix properly. IIRC, the Buderus has some sort of a velocity stack on the intake, have you tried restricting the opening on that? (Think duct tape) Or how about removing the stack and checking the result. Very interesting noise from a boiler that is usually very quiet!
  • Chris_82
    Chris_82 Member Posts: 321
    right on darrell,...

    As Darrell points out: the air is already close to saturation, Mark is presumably already at 6,000' (?) feet. It's not so much the velocity is further cooling air that is close to being saturated and this precipitates¡¦ condensation, actually latent heat is released under these conditions, but the increasing velocity reduces air pressure, this redux in pressure brings the close to saturated air to the existing due point, the same as a further increase in elevation would, (it's called forcing the LCL,) and the moisture condenses, it has to. It is also the reason why it collects so readily on the screen; it is at this point that the air pressure is maximally reduced as it travels around the wire mesh. Removing this mesh is a solution, but perhaps not the total cure. The other solution as Darrell is getting at is to reduce the air velocity; the only way you can do this is to enlarge the opening. And hope the dew point/ condensation transition takes place in a warmer environment, i.e. closer to the boiler where the readily warmer air can hold more moisture. Multiple intake vents? Or as I begrudgingly point out the standard Munchkin boiler comes with a "T" as its intake fitting. This accomplishes the same as the above increasing the size of the intake as already mentioned. On another note, is there any chance that this unit is in some sort of test mode? Even at max demand the fan throttles back within a few moments? That sound, sounds like it is running at full tilt constantly? If it were a Munch, you know what I would recommend inspecting even if it was right out of the box ƒº :)
  • Joannie_12
    Joannie_12 Member Posts: 42
    Frost on Terminal

    Hi, Mark.

    Our Canadian guys saw this on a larger commercial unit. I'm not sure what the outcome was, but I'll check. As I recall, it wasn't anything to do with the vent exhaust. This type of frost happens elsewhere (as Brad mentioned, we see it on Mt. Washington...it forms on their monitoring equipment and they have a scheduled maintenance system, in which poor **** that work up there have to walk out and knock the stuff off of the equipment.)

    If I find anything more out about the Canadian unit, I'll let you know.


    Laars Heating Systems
  • Ricky Rocket to the rescue....

    The Meek shall inherit the Earth...

    Rick Meek from TM Sales met me at the job with a pump supplied by Dennis Bellanti of Ferguson Fame. Replaced the 2664 with a 2699 and the airplane has left the boiler room. Whooda thunk.

    When I get ahold of that clown that sized this pump, I'm gonna give him a peice of my mind... Wait a minute, I sized that pump... OOpppss....

    Thats what happens when you choose a different delta T than the manufacturers chose and the tank and the boiler logic don't communicate real well. Micro bubble steam flash due to low velocity and consequential boiling/bubbling.

    If it hadn't had glycol in it it probably wouldn't have been a problem.

    In the words of the late great Gilda Radner, "NEVAH MIND!!!"

    Thanks for your help Rick and Dennis.

    Side note, the security text for entering this post is DUMueJpx. Think someones trying to tell me sumpthin'???

  • tom k_4
    tom k_4 Member Posts: 10
    Please let us know if this also solved the intake prob,...

    I love the owners manuels that come with these units, not to disparage other manufactureres but in comparison they set a standard that is hard to beat. Has the high altitude kit been installed? And is there a particular reason, you can't just use inside air for the intake? pgs 17-21 in the man. I don't see the u tube type intake shown in the man., either but I cn understand the snow logic getting into the intake, ya I know about air infiltration and positive /negative pressure...and I can't tell from the picture but are the flu gas adaptors installed? on another note can we see which condensate unit u are using, and I can't see if the reccommended LWCO is there? Let us know the resolution of the intake problem :)
  • Ted_5
    Ted_5 Member Posts: 272
    In Germany

    they do not vent this way! Everyone says that Buderus sold thousands of these boilers before they came to the states with a good track record? If they are not same then how can you compare? I saw this boiler in the Buderus booth at the ISH 2 years ago and the only vent option was a pipe in a pipe. Do you think this would help this problem? How about vent adaptation logic? Or would that add to much cost? It would correct that problem and maintain Co levels at the same time. Do you think proper air to gas mix is important to combustion and efficiency? or is that another topic?

  • Tom K...

    The bigger pump would not/will not address the frost blockage. At present, we have taken the platic seal that sits on the top of the appliance off to allow for inside air for combustion and have had no issues since. As for the venting question, its right out of the installation manual, page 21 (see attached picture).

    The flue gas adaptors are on top of the unit.

    On this particular job, my brother did the DWV and it is ALL done in non foam core PVC piping, all the way to the plastic septic tank, so I saw no need for a neutralizer and therefore did not use it, and the code authority concurred. When we are required to neutralize, we have a neutralizer that my partner came up with that is about 1' tall, made of 4" PVC, capped on the bottom, with a removeable cap on top for checking/filling/replenishing the neutralization material (marble and limestone), a tee near the bottom and a tee near the top, condensate is fed into the lower tee and eventually trickles out of the top tee to an indirect drain. In field testing, it raised the pH to 7.4 from an initial low of 4.5

    There is a LWCO installed on the highest piping serving the boiler.

    Once the snow leaves the roof and safe access can be made, I am going to climb back up there and install a 4 X 3 increaser, then a 4" bull headed tee with the run horizontal, and am going to throw an additional 1" on top of the exhaust just in case recycling has been occuring.

    You mentioned high altitude kit. Enlighten me please. I was under the impression that these boilers are self compensating as it pertains to altitudinal density changes.

    Am I missing something here?

  • Ted

    I think a concentric vent probably would alleviate frost build up due to heat migration betwixt the exhaust and intake, however, the concentric venting kits currently available were actually meant for horizontal applications, and we can not comply with the need to keep our intake 1 foot above highest anticipated snow levels without having two penetrations thorugh the roof, which kinda defeats the reason for using concentric venting any way.

    I am under the impression that if the exhaust or intake air are blocked that the burner automatically adjusts any way, and yes proper air to fuel ratios are critical and MUST be tested, adjusted if necessary and documented at the time of appliance commissioning.

    If you're not testing, you're just guessing and someone could die as a consequence. I know I could not live with that on my conscience...

  • Chris_82
    Chris_82 Member Posts: 321
    is this it?

    Not shure if this is your model?

    See attached...
  • That is it...

    Where did you get that from. It's not on their web site and it wasn't in the installation manual on the site...

    BTW, the numbers from the combustion analysis were just fine. If they had not been, the unit would not be running right now.

    EBEBRATT-Ed Member Posts: 15,348

    What about increasing the size of the inlet pipe to slow the velocity?? I think thats what Lennox use to do with their pulse furnaces when they had a similar problem.

  • S Ebels
    S Ebels Member Posts: 2,322
    Haven't checked this for a couple days..........

    Mark, I've had two installs, both furnaces, that had the same recurring issue that you have there. In both cases the only location for the vent termination was less than ideal. One was near an inside corner behind some shrubbery the other one was through the roof near a dormer. Both appliances were vented in 2" PVC per manufacturers guidelines. We changed the intake from 2" to 4" at a vertical point inside the conditioned space. This moved the "venturi" point back inside the buidling where the hoary problem did not raise it's frosty face. It would probably work in your case also. Not a great alternative but better than repeated call backs.
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