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Strange residue in Giannoni heat exchanger

BillatbhBillatbh Member Posts: 2
Hello, Tim.  There is this strange combustion residue build-up happening in gas fired boilers (don't know about propane) with the Giannoni-type heat exchanger which has flat stainless steel coils spaced close together forming a cylindrical combustion chamber.  The cylindrical surface burner resides in the middle of this.

The residue looks variously like coffee grounds or mouse droppings.  It builds up and blocks flow of combustion gasses, affecting efficiency and soon bringing the boiler to a stop.  Some boilers produce a lot of it, some very little.

I can't get the boiler manufacturer to admit knowing what this stuff is or why it should form only in this type of heat exchanger.  They tell me it has to be something in the gas as they know this doesn't happen in Europe with the same product.

Do you know?



  • Tim McElwainTim McElwain Member Posts: 4,372
    I have my theories

    about corrosion and coffee grounds along with other residue being found in Giannoni Heat Exchanger Appliances.

    1. I feel the using PVC and CPVC venting is causing a reaction on shut down due to residual heat build up and the chloride breaking down due to over temperature in the plastic and then getting getting back into the combustion area. I realize when stating this that plastics are inert but I feel exceeding the maximum temperature of these plastics will cause this breakdown.

    2. With DHW (higher temps on condensing/modulating boilers) off the boiler this may increase the likely-hood of this PVC/CPVC breakdown.

    3. The failure to carry out yearly maintenance and cleaning of the equipment.

    4. Improper installation and piping arrangements

    5. Running at constant high temperatures for baseboard applications. There should be outdoor reset on all of these setups along with added baseboard for running at lower temperatures.

    6. Failure to properly setup the combustion with an analyzer. Or to strictly following the manufacturers guidelines instead of firing the units at maximum firing rate and observing O2, stack temperatures and CO readings and adjusting throttling controls for proper air entrainment an d maximum efficiency.

    7. Poor quality fuels may also cause this with both LP and Natural gas or the mixing of LNG with pipeline distribution gas (natural gas) the LNG perhaps having a higher BTU content.

    8. Increased levels of Etyhyl Mercaptan odorant in both natural gas and LP.

    9. Is the air from outdoors always pure, sprays for lawns and shrubs and other fertilzers used outdoors getting into the air mix.

    I feel it is any of these or a combination of them. I have not heard anything from any manufacturers as to what they think it might be. I would hope perhaps some others here on the Wall may pick up on this posting with perhaps their theories or maybe someone has some tested facts?
  • Bill Clinton_6Bill Clinton_6 Member Posts: 35

    Hi, Tim:  I don't see much support for the pvc/cpvc theory.  I've been installing condensing heaters (Hydrotherm Pulse, Polaris, and Voyager) with plastic vents for twentyyears and never seen this stuff 'til now.

    Failure to perform annual maintenance is not the cause.  This stuff can be so bad as to cause ignition failure BEFORE the first annual maintenance is due.

    Combustion analysis and proper setup are important, and we do them, and the stuff still appears.  Also, we have serviced many of the above named appliances that were way out of adjustment and the stuff isn't there.

    You'd think the manufacturers would do some chemical analysis and find out what it is.  Maybe they have and they're not telling us.

    In the mean time, I'll just use boilers with heat exchangers that don't do this.

  • Mark EathertonMark Eatherton Member Posts: 5,843
    Just curious Bill....

    What mod con have you found that DOESN'T get these byproducts of combustion on them?

    The Viessmann's I've worked on get them. Haven't had to service any Triangle Tubes, 'cause they say they don't need serviced annually.

    Aluminum boilers get a grey yucky gook in their traps.

    Someone was showing pictures of mod cons, specifically Gianonni with crystals growing inside, but he was close to the ocean (west coast), but have talked to east coasters who hadn't seen it.

    Am not exactly sure, but I seem to find more junk in boilers operating near high traffic areas. Maybe dust in suspension?

    You might try an air filter to see what affect that has, if any. Remember, Glow Core's had filters on them. Maybe they knew something the others don't...

    At one point in time, I was told by a manufacturers rep (who shall remain nameless) that it was coming from the heat exchanger, and that it would eventually pin hole and fail.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Tim McElwainTim McElwain Member Posts: 4,372
    edited October 2009
    Bill and Mark, I am getting reports

    from different folks doing annual maintenance on these units and there are sporadic reports of green deposits, hard mineral like deposits, coffee grounds deposits, dark grey matter in the bottom of the heat exchanger, and stainless steel coils with signs of pitting.

    The Ray by the way does have a built in filter for air flow from indoor or outdoors, maybe they know something?

    I had one of my students who had an aluminum heat exchanger boiler which he was not aware needed cleaning. He went home from class that night and pulled open his unit, end result he needed a new heat exchanger. It had gone five (5) years with out maintenance
  • eluv8eluv8 Member Posts: 174
    edited October 2009
    Coffee Grounds

    Coffee grounds, as explained to me are a result of the target wall being exposed to high humidity in the combustion chamber causing deterioration in the material. Depending on the manufacture these coffee grounds can be very toxic so handle with caution. Common cause is from an obstructed condensate drain or the heat exchanger itself "not the boiler" is leaning forward enough to cause puddling or low flow to the back of the combustion chamber. I have seen level boilers that had a heat exchanger leaning forward enough to cause problems. You must put a torpedo level on the heat exchanger manifold itself to be sure. Ideally kick the heat exchanger back 1/4" to be safe, and make sure that the coffee ground material has not plugged anything up in the condensate system. I had a boiler that this material plugged up the float on a condensate pump and it would not work properly causing intermittent lockouts.

    Edit: Yes there is a certain amount of material that will leach out of the stainless during the combustion process, usually seen as hard black specks on the heat exchanger. The leaching has been taken into account in the design of the heat exchanger under normal use and following the recommended flow rates and water quality has an expected life over 15 years and more depending on which Giannoni heat exchanger is used and its application. They offer multiple types and wall thicknesses depending on who they are making the heat exchanger for and its application. Not all Giannoni heat exchangers are the same from manufacture to manufacture.
  • Tim PotterTim Potter Member Posts: 252
    Something new to blame !!!!

     The response from Mark is interesting...

    "Am not exactly sure, but I seem to find more junk in boilers operating near high traffic areas. Maybe dust in suspension?"

    A few years ago there was a 'group' claiming that the rubber that was worn off tires was contributing to: (Fill in the blank_______). They were supposing that because we drive X amount of miles per year times however many cars are out there that all that rubber that is worn off the tires must do something very bad to something. They didn't find any connection to any health concerns, tire particles are inert, but The funny thing is, that they still didn't know where all those rubber particles went. They apparently don't pile up on the side of the road. Hmm... 

    Tim (the Tire Guy)
    Winter Park, CO & Lenexa, KS
  • Tim_HodgsonTim_Hodgson Member Posts: 60
    Coffee grounds in giannoni heat exhangers

    I agree with Mark that all condensing boilers have some scale on the fireside. I too have noticed some units require cleaning twice a year. The manufacturer said to clean it with CLR (phosphoric acid). I took a cup of it back to the office and stuck a magnet in it. Wow! it is ferrous. The R in CLR is for Rust. My observations are the combustion air pipe is usually in a damp area (flower beds, shrubs and bushes) there may be some extra recirculation of moist air. Although I have not noticed any evidence of moisture in the boiler cabinet. My best guess(and yes that is all it is) the stainless is not as high a grade as it should be, but wait it could be the landscaper using too much moss out on the lawn..... Of course I have not found any magnetic scale particles in an aluminum heat exchanger.

    I have found through the years that if a manufacturer minimizes the problems and sells the benefits. So if I hear them say they have a minimal problem, it is probably the weak link in their equipment. The same thing holds true for the installation literature.
  • Jr_12Jr_12 Member Posts: 38
    I Always thought

    That the "coffee grounds" were impurities in the gas. If they are in fact magnetic, then it could be from the gas pipe making it's way through the blower/burner..?
  • Brownie99Brownie99 Member Posts: 7
    edited April 2013
    Gianonni in Europe

    The same problem exists in Europe - Here is a photo of a UK heat exchanger 6 months old.
  • SWEISWEI Member Posts: 7,356
    that sure looks ferrous

    have you put a magnet on it?
  • Brownie99Brownie99 Member Posts: 7

    We are carrying out investigations now and will test it and let you know the results.

    I have worked at a major boiler manufacturer for 25 years until recently and what is apparent is condensing boilers are OK if you don't use them in the condensing mode.

    Aluminium boiler block the heat exchanger after 2-4 years on the combustion side by leeching salts which collects and solidifies. The major suppliers of aluminium heat exchangers are looking at coating the aluminium and I believe Buderus already have this technology.

    On the steel boilers with the Gianonni heat exchangers the blocking above and brown condensate is now found to be the norm for boilers in the condensing mode with failures occuring by pin holes after 12 months.
  • CMadatMeCMadatMe Member Posts: 3,066
    Common Sense

    When talking about alum HX's. Low PH and Alum = Corrosion and you cannot get away from it. You can though, slow the process down when chemicals. Weil has been providing it with their alum block boiler for quite a few years now. Took them some time to add it, guess the failures began to add up.

    I might lean towards Tim's thoughts as to PVC/CPVC venting as a contributor. Stainless steels biggest enemy is Chlorides and when stack temps get elevated for what ever reason (which there are many) I believe chlorides from the PVC/CPVC leaches back to the HX and accelerates corrosion.

    To say condensing boilers are OK if they don't condense is in my opinion a foolish statement.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Paul48Paul48 Member Posts: 4,492

    Even if the manufacturers discover the PVC and CPVC to be the culprit, don't expect them to own up to it. The "Class Action" law suits would bankrupt them.You'll just begin to notice it disappear from approval, which some will say, should have happened long ago, anyway.
  • HenryHenry Member Posts: 968
    Clorides leaching

    We have opened my mod-cons installed by after two years. There are no coffee grounds. We did have heat exchanger failures on installs by others. The cause of several was:

    Blocked neutraliser, thus flooding the combustion chamber

    Exhaust gas recirculation (somehow the utility repair company did not figure it had a problem when in one case, it replaced a dozen hot surface ignitors!)

    PVC or CPVC leaching and the coffee grinds were only found here, in boilers that had improper vent and combustion air terminations. The boiler would suck slightly corrosive and warm gases which would release some chlorides. There is so much restriction in the heat exchangers, there is no way that combustion gases and leached chlorides could end up in the heat exchangers.
  • Brownie99Brownie99 Member Posts: 7

    The experience I have on the boilers is approximately 400 sites with an average 4 boilers per site split 50/50 Aluminium / Stainless. We changed from the Aluminium boilers 5 years ago due to the combustion side of the heat exchangers blocking u after 3-5 years.

    The flue system used have been plastic , aluminium and stainless steel. Stainless steel flue on Aluminium boilers is a known problem as any condensate running back into the boiler that has been in contact with the stainless will attack the Aluminium and cause failures in 6 - 12 months. New boilers have a drain at the flue spigot to overcome this.

    On the stainless boiler we have predominately used the manufactures fklue with a plastic liner.

    These boilers are used in a special process with water temperature of 20 to 30C on the return which should be ideal for condensing boilers.

    Some of the older sites use a primary loop at constant temperature 60C and variable temperature secondary due to mutiple streams and unfortunately do not operate in Condensing mode - It on these sites we have not had a problem with either Aluminum or Stainless hence the comment re condensing mode.
  • Tom_133Tom_133 Member Posts: 689
    Wow, would not have guessed

    I completely follow Brownie's statement "condensing boilers are OK if you don't use them in the condensing mode. "

    My scenario: I currently service 2 boilers both propane units, installed by others, one is piped old school, that is 4 zones, that is 4 circs and no primary loop just like you would pipe a non condensing. We will call that boiler 1

    The other is 2 zones all radiant in the slab it's one level, piped primary secondary. Typically runs at 90 degrees for 6 months at a time. Thats boiler 2

    Boiler 1 after 3 years of running needed tuning, customer called and said this thing is thumping a little on take off, so I went there and popped open the heat exchanger, WOW, clean as a whistle. Turns out the installer had pitched the vent pipe the wrong way and it was so long out of the wall that it kept freezing so the customer removed the factory exhaust tip (concentric venting on both units, both units are the same manufacturer) so it was sucking in it's own filthy exhaust air. Fixed vent pipe pitch and tip and did calibration on combustion.

    Boiler 2- The first time I showed up the boiler wouldn't run at all and so I pulled apart the Hx and it was full of the coffee grounds and scale junk. I cleaned it thoroughly (I use a toilet brush and water) and it ran great so before adjusting anything I checked the combustion, and it was spot on to the manufacturers spec's. I mean SPOT ON. I assumed it was burning bad and that's what caused the plugged Hx, but 2 years in a row that heavily condensing boiler has plugged solid, so I totally get Brownie's statement.
    Montpelier Vt
  • Brownie99Brownie99 Member Posts: 7
    Heat Exchanger Deposits

    The deposits are magnetic.
  • SWEISWEI Member Posts: 7,356
    edited June 2013
    Magnetic coffee grounds

    If there's no other ferrous material in the fire side of the system, it must be coming out of the stainless HX.  That would considerably weaken the HX -- are any of them leaking?
  • Jean-David BeyerJean-David Beyer Member Posts: 2,663
    My observations are the combustion air pipe is usually in a damp area

    I just measured mine, and the combustion air pipe is 8 feet above the ground, and about 3 feet higher than the deepest snow I remember around here. Since my heat exchanger is aluminium, I do not expect to find ferrous particles in the condensate trap. When the tech comes out each year, he takes the front off the heat exchanger, inspects it, cleans it, replaces the igniter and its gaskets, and replaces the front of the heat exchanger and its gaskets (all new gaskets). He also takes off the condensate trap and examines the crud inside. Nothing I would call coffee grounds. The first year, he was a little alarmed at what it looked like, and had it analyzed for aluminium. There was a little, but nothing to worry about he said. In the next few times there was next to nothing in the condensate trap.

    This spell checker insists it is using the US English dictionary, but it seem to be using a British one. Color or colour? Advertizement or Advertisement? Nope: it is using British.
  • Brownie99Brownie99 Member Posts: 7
    Heat Exchanger Deposits

    I have not yet come across any heat exchanger's leaking yet due to the deposits and some of the installations are now > 5 years old which is the manufacturers warranty period in the UK. The contamination causes the boiler to automatically down rate due the back pressure in the combustion chamber, the normal symptoms indicating a problem are flame failure on start up. Once the heat exchanger is cleaned the boiler works fine until the next service.
  • Jim Davis_3Jim Davis_3 Member Posts: 578
    Post purge?

    Has anyone tried to increase the timing on the inducer when the boilers shut down?

    Anytime I had any gas induced draft appliance or forced draft, if the post-purge wasn't at least 3 minutes there were problems.

    This cannot be provided by the manufacturer because of the penalty deduction from their AFUE rating.

    This is hard to do on variable speed inducers but most here are smart enough to figure it out.
  • SWEISWEI Member Posts: 7,356
    So where is the iron coming from?

    I'm genuinely curious.
  • SpeyFitterSpeyFitter Member Posts: 422
    Slo-mo post purge

    I know on IBC and Cleaver-Brooks Clearfires that after burner shut down and a regular post purge the fans go into super slo-mo post purge mode for around an hour to 90 minutes. Correct me if I'm wrong but I believe this is to keep any humid/condensate laden air from going back into the fan, as well as to slowly drive this humid air out so conditions are more favourable for the next burner ignition. This is supposed to really help reduce fan failures over time apparently. Do any other manufacturers do this?
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • SpeyFitterSpeyFitter Member Posts: 422
    Me too

    Has anyone sent these heat exchangers (when they fail) to a metallurgist for investigation? The Giannoni heat exchangers if I'm not mistaken have 0.7 mm thick tube walls so theres not much beef there to deal with any corrossion issues.

    If I recall correctly from training a few years ago, IBC sent a 12 year old heat exchanger (downfiring water coil design made of 316ti Titanium stabilized stainless steel, Giannoni's use 316L stainles steel) to a metallurgist for analysis to assess how it was standing up and it only came back with only some micropitting which is basically the equivilent to virtually nothing.
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • SpeyFitterSpeyFitter Member Posts: 422
    Pvc or cpvc?

    Was that above boiler vented with PVC or cpvc? Do they have PVC or cpvc in the UK for venting?
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • Brownie99Brownie99 Member Posts: 7
    Gianonni in Europe

    The Giannoni heat exchanger we are using were assumed to be 316 grade but enquiries with the manufacturer have revealed they are 304 grade. It may be that the grade has changed for commercial reasons and that is why the problems are now being observed.
  • SpeyFitterSpeyFitter Member Posts: 422

    Interesting -a quick search does indicate some manufacturers are using 304L S/S Giannoni heat exchangers. I believe most in the USA that use the Giannoni are 316L though (correct me if I'm wrong). I know the 316L is supposed to be better than 304L in general but we still don't know where the accumulation is coming from.

    I know on Vitodens heat exchanges, and IBC heat exchangers, they see the same or similar type of accumulation over time (although I've never see one that plugged or that bad as the one pictured). It would be interesting to have this debris compared to see what differences there are between boilers/types of heat exchangers as some use different variations or types of stainless (439, 316ti). If it is the same chemical make up then it points towards combustion or condensate related impurities or issues, perhaps Mercaptain, or sulfur, where some reaction is occuring that creates it. Or is it indeed a stainless steel phenomenon and not present in aluminum heat exchangers like on the Buderus?
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • JJSJJS Member Posts: 3
    Coffe Grinds...

    Just ran into this thread -- hoping some are still following.  I design heating systems -- for about 28 years now -- recommend various manufacturers of boilers and have had a rather tainted past with the condensing boilers.  Here is what I have gathered...

    The grinds are a mix of the ferrous elements of the stainless exchangers (manufacturers have had them analyzed) -- foreign particles in the air - little effect to them - dirties up the burners though.  Some have said the sulphur from the gas -- some have said the refractory -- I'm leaning more and more to the stainless.  All I have ever vented with is stainless and I've had lots of issues so I can't give the CPVC thing too much myself.

    I have definitely seen the boilers running low temp infloor (condensing) fill up 2 or 3 times a year -- the boilers running up 160df and up -- all clear.

    The refractories in the back soak up moisture big time -- lots of failures...

    Interesting to me -- the boiler models with the burners in the top of the "double exchanger" don't seem to me to give the same level of effect -- drier top exchanger??  I can't say I've seen enough triple exchangers yet to compare top to bottom operational differences.

    I like the note on the purging -- very interesting idea I'll have to try.  I've not noted the extra long purge time on anything unless they promote common venting (one of the worst ideas in my mind - typically nothing but heartache from my point of view)

    Aluminum exchangers -- I'll agree with all the above -- pro's and cons.

    Sorry for the run on -- this has plagued me for a while - refreshing to see the other notes - anxious to find a solution (other than stop using Giannoni's)
  • Plumdog_2Plumdog_2 Member Posts: 873
    For what it's worth...

    I find the mouse turd/coffee grounds more abundant in boilers that condense regularly; like those with outdoor temp compensation and connected to radiant systems. The grounds are laying on the top of the burner, and piled up in the bottom of the exchanger. Boilers set to 180 degrees don't pile up near as much. But they get stubborn scale buildup. 
  • Brownie99Brownie99 Member Posts: 7
    Heat Exchanger Deposits

    We have been investigating the deposits in the UK and a large number of sites by comparing hours run and mode of operation. We have only found the deposits on sites where the boiler operates in the condensing mode and on high use sites the boilers have required cleaning every 1500 hours of operation which ties in with previous comments. The gas supplied is from several different sources so it tends to discount this as an external influence. Again it appears to be a chemical reaction with the stainless steel that is left as the cause. With regards to the refractory absorbing moisture we have experienced several failures of the refractory with a tide mark visible, this is because the deposits are washing through and blocking the condensate trap causing the boilers to fill with condensate causing boiler faults with loss of flame during operation. We have experienced burner bar failures due to the deposits glowing red hot and radiating back on to the burner, inspection of the burners shows the inner galvanised baffle has melted, leading to light back and then failure of the outer burner tube. We have not yet had a heat exchanger failure due to the problem and the field stock is up to 7 years old. We have hd no response from Giannomi and have had to accept the issue is managed by maintenance.
  • JJSJJS Member Posts: 3
    Coffee Grinds...

    Thanks for the input Brownie99 -- have you noticed by chance any correlation between exchanger materials -- some folks use 316Ti as opposed to the 316L -- have you seen the same deposit issues in any of them??  If I look up the 316Ti material properties it definitely seems to be able to handle the high temperatures better and may not succumb to the loss of the ferrous element.
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