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Thread: Humming/groaning sound when boiler kicks on

  1. #1
    DIY Member BillTheEngineer's Avatar
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    Default Humming/groaning sound when boiler kicks on

    A little info:

    I have a High-ranch style of home, 3 heating zones, with fin and tube baseboard convectors. The boiling is a early nineties gas files 2 stage boiler (Raypak H3-0125B, see photos). When I turn the thermostats up and the heat is just kicking on there is a some humming/groaning, I am not sure if its from the circulator coming on and the water getting up to speed through the system or because it's being heated or a combination of the two. THe noise also happened more often when just one zone (living area, not bedrooms or lower level) cycles on. It seems to make noise when the thermostats call for heat and it goes away in a minute or two.

    I found the manual for the boiler and there is a valve between the inlet and outlet of the boiler and it states:

    The boiler is supplied as standard with a circulator
    and a built -in by-pass to insure the required minimum
    water flow in the boiler. The by-pass on models H-0135
    and H-0180 is provided with an adjustable valve that is
    factory set in the full open position. The handle is
    shipped loose. The full open position is appropriate for
    most systems, and insures adequate flow through the
    boiler. If system flow is inadequate, (indicated by
    excessive temperature drop through the system) the bypass
    valve can be throttled slightly. Care must be taken
    against over throttling which may lead to inadequate
    flow through the boiler and boiler harmonics (a humming
    sound from the heat exchanger). If adequate system
    flow cannot be obtained without causing harmonics, an
    additional pump is required. The factory mounted
    circulator will provide adequate water flow for systems
    designed at a 20F temperature drop, and system
    pressure drop or head not exceeding that is shown
    below.

    On my system the circulator that supposedly came with it is no longer there and there are Taco 007 circulators for each zone.

    I have tried adjusting the valve between the boiler inlet and outlet and the system still makes noise. It seems like the noise is more prevalent when just the living area zone is on and the other two zone are cold.

    I have recently replaced the relief valve, feed water regulator, and air eliminator (neither was working properly) and bleed the system and got most if not all the air out.

    Any ideas as to figuring out the humming?

    Also I believe this is a two stage boiling with two firing rates (yeah I know both are probably a lot higher then what is needed), but how does it determine with rate to fire at?

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  2. #2
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    This is a low-mass copper fin boiler with cast iron headers and will act much like the newest low-mass high efficiency condensing boiler if minimum flow rates are not maintained while the unit is firing; it will kettle. Most boilers will require minimum flow determined by the pressure drop through the boiler regardless of calls for heat or circulators running. If it goes to high-fire on one long or restrictive zone with single circulator it may kettle. Inversely, if all zones call and all circulators are running energy is wasted and velocities may cause other problems.

    If it worked fine before we would look to the circulator performance. We prefer a single pump with differential by-pass or ECM pump properly sized and never push an expansion tank, scoop and vent as you see here and so many other places.

    Most two-stage gas-fired boilers step-fire on temperature.

    By the looks of the boiler it is time to shop for a new one.

    PS. Air in the pipe will result in poor heat transfer and often makes low-mass copper boilers kettle.
    Last edited by BadgerBoilerMN; 11-22-2013 at 05:29 AM.

  3. #3
    DIY Member BillTheEngineer's Avatar
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    Is there a way to differentiate weather the harmonics of are from the velocity of the water flow or if there are from kettling (boiling)? I am no expert, in this area, but I would assume the kettling would be louder as the water boils and then collapses, just guessing. I am thinking it's more of a water velocity issue or a thermal shock/transient related.

    Just from what I have noticed:

    -with the valve (the one between inlet and outlet) open the humming is not to bad. The noise happens when there is a call for heat and the boiler is cold (~60F from sitting off all day). There is also a noise when there is a call for heat and the boiling in the typical operating range (~150F to ~190F), the noise does not happen all the time and it's a little quieter and does not last as long, as compared to when the boiler starts from cold or if the valve is closed.

    -with the valve (the one between inlet and outlet) closed the humming is noticeable worse, louder and lasts longer. The noise happens when there is a call for heat and the boiler is cold (~60F from sitting off all day), it's louder and lasts longer. There is also a noise when there is a call for heat and the boiling in the typical operating range (~150F to ~190F), the noise does not happen all the time and it's a little quieter and does not last as long.

    I have looked over the manual a little more and have noticed that are a few things that don't really follow the mfg's recommended installation. As BadgerBoilerMN, said the expansion tank/ air scoop and not is the correct location, they should be on the return line. There is no automatic vent damper, I believe it came with one. I also believe there was a circulator on the return/inlet from the factory, it's gone too.

    out of the manual:
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    The only other change I can that has been done is the ignition has been changed to a hot surface igniter.

    Other than being a little dirty and not really correctly installed, what suggests that it's time for a new boiler? I would really like to, but as I just purchased the home, I would prefer to hold off a little and not blow my oh crap fund. Unless it starts leaking I have no plans on replacing it, at least in the next couple of years. I would consider re-plumbing it, if that is the only solution. My future plans would be to replace the gas hot water heater with an indirect and also replace the boiler with a mod/con or just a more efficient boiler (properly sized).

  4. #4
    In the trades Dana's Avatar
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    One symptom of low-flow would be a sustained high temperature differential between the water coming back from the baseboard and the temp of the output of the boiler. Most reasonably designed systems would run with less than a sustained 30F difference no matter how many zones were/weren't calling for heat, with a 20F nominal (as specified in the manual.) I couldn't find a manual on-line, but if it bumps up to high fire based on a low delta-T and the temperature sensing was off it might over-fire for the lower flow of a single zone.

    With the original pump configuration the bypass loop was acting as the hydraulic separator, with the boiler flow determined by the near-boiler pump, and the radiation flows by the zone pumps. Without the near-boiler pump in the system you'll get more flow through the boiler if you CLOSE the ball valve on the by pass branch. Measure the delta-T, which would tell you if it's getting anything like the right amount of flow with just one zone calling for heat. (Infra-red thermometer readings of the iron in/out pipes at the boiler would be close enough.) You should be able to adjust the delta-T on the boiler downward (and boiler flow upward) by throttling back the valve on the bypass branch. If you can't get the delta-T under 30F with just one zone calling for heat, it either needs more zone-pump, or it needs the (currently absent) primary loop pump.

    Measure it, but before you start hacking away buying pumps and hacking on the near-boiler plumbing, consider this:

    The nameplate seems to indicate that it was manufactured in 1987- after 26 years of service this boiler doesn't owe you anything, and it's probably running below it's nameplate efficiency at this point. This boiler is at end of life, and while just nursing it along with repairs on a regular basis can probably keep it going, the mid & long term economics of that approach aren't favorable. Waiting for the catastrophic failure isn't in your best interest.

    The time for figuring out what you are going to replace it with is well BEFORE you have a steaming puddle hot water all over the slab or a freezing cold house, so that you have time to really consider it and end up with something appropriate. You're right that even at low fire this thing is probably 2x oversized for a 2500' rancher on L.I. . But whether a mod-con is the right solution depends- if you're really running the thing at 150-190F with reasonably long burns during milder fall weather you may not have enough radiation to get much in the way of condensing benefits, especially if it's chopped up into three stubby zones of fin-tube to short to be capable of running at condensing temps without short-cycling the boiler. The right thing to do is figure out what it needs, what it costs now, and apply any hardware-upgrade money to the next boiler, not in trying to fix this implementation. Then even if the thing decides to croak before you really wanted to spend the money on a new boiler, you'll have the right plan, and not be scrambling to figure it all out under pressure, and getting stuck with an inappropriate boiler, poor implemented for the NEXT 25 years.

    Do at least the following napkin-math:

    While it's still running, as an easy preliminary you can determine the boiler sizing by charting fuel use against heating degree-days. It's been pretty mild the last month, if you do it with your most recent bill it may be a bit off (but probably not by more than 10-15%)- the next gas bill is probably good enough. If your gas company prints the average temp over the billing period an the average therms or ccf per day, that makes it dead-simple, but otherwise you can look up the heating degree days between the billing dates on degreedays.net, and come up with a therms/HDD number. Multiplying by the 0.80 or 0.82 efficiency rating give you the BTU/HDD. From there you divide by 24 to come up with BTUs per degree-hour. The 99% design temp for L.I. is +15F, and using a presumed balance point of 65F (the presumption behind a 65F base for heating degree days) you have (65F-15F=) 50 heating degrees. Multiply your BTU/degree hour by 50 and you'll have a boiler-measured BTU/hr heat load.

    The ways this method has any significant error is if you spent a couple of weeks in Belize and had left the thermostats at 50F, you have a very high-R house with a lot of passive solar gain designed in, or you take 8 showers a day, draining the hot water heater, etc. Otherwise it's a reasonably accurate stake in the ground to work with, from a boiler sizing point of view.

    If you take than number and divide by the total length of the fin tube baseboards you'll have a max BTU/foot number to work with, which will determine how much condensing efficiency you might get, provided the lengths are long enough to keep from short-cycling the boiler. If you use our calculated heat load number number, and look at some boilers with a maximum fire output just a tiny bit higher than that, look at the min-fire numbers of those boilers. Fin-tube only puts out 200-250 BTU/hr per foot at condensing temps- if the length of fin-tube on the shortest zone multiplied by 250 BTU/hr isn't well over half the min-fire number of the boiler that's sized for your heat load, you may have to combine zones or add radiation or add thermal mass to the system to get condensing efficiency without burning out the boiler by short-cycling it.

    There is always a way to get there, but at different price/performance points, and you may opt for a straight ahead mid-efficiency cast iron pig of a boiler with some heat-purge control lipstick to guarantee it hit's it's numbers rather than a more expensive mod-con. But either way, it's better to have a good handle on the reasonable options before things get dire.

  5. #5
    DIY Member BillTheEngineer's Avatar
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    Here is a link to the manual


    After watching it few times when the humming was more pronounced, I think you correct that it's kettling (boiling). When there is a call for heat and the boiler is cold, I think it goes into the higher firing rate and the water flow is low till the pump has some time to get the water flowing. The humming is only for a minute or two at the most. If two zone are calling for heat and the humming does not happen either.

    So my thoughts are:
    1- measure the temp difference between in and out
    2- connect both upstairs zones in into one (change the thermostat wiring so if either calls for heat they both come on)
    3- if not 2, is there a way to have the system only work at the lower firing rate? I would think this would sufficient even on the coldest windiest day, might just take a little longer to raise the house temp.

    I really don't have plans to re-plumb the system anytime soon, unless something fails. But in the mean time I will do a manual J and might get a blow door test too. I only purchased the home in July, so I would prefer not to blow my oh crap fund, I would rather save some first and then update the boiler and HW.

    I am assuming that its ok for this boil go cold regularly, as when I am work the thermostat are set to basically off. And even when I am home the heat does not kick on to often.

  6. #6
    In the trades Dana's Avatar
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    Water tube finned heat exchanger boilers are always fine for cold-starting, unlike some heavy cast-iron boilers.

    Given it's age, condition & symptoms, the boiler a likely prospect for becoming the expenditure in the "oh crap" fund- band-aid it as much as you can, but start saving up soon.

    Don't be surprised if the Manual-J indicates the basement as being one of the largest heat loss areas. There are several ways to air-seal and insulate basement walls at a variety if price/performance point. It has to be done right to avoid making a mold farm, and some of the variations are climate-specific. (I've covered that multiple times on the remodel forum of this site and elsewhere.) In my own 1920s vintage home insulating the basement walls, foundation sill & band joist resulted in a nearly 20% drop in fuel use per heating degree-day, even though the basement now runs warmer than previously.

  7. #7
    DIY Member BillTheEngineer's Avatar
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    I understand the spending on band-aiding and really would prefer to save money and put it toward a new boiler, but in the mean time just looking for way to buy some time, before needing to raid the oh crap fund.

    If i could figure out how to have the boiler run at just the low output level, would this cause any harm? or would it shorted the time between now and when the oh crap fund would need to be raided?

    Reading the manual and looking over the wiring diagrams, wondering what actually controls weather to fire at the low or high setting?

    I see a 2 stage controller in the wiring diagram, I assume this is what gives a signal to the gas valve to determine what the firing rate should be, is this correct? How does the 2 stage controller work? is it just a timer? is it looking at in and out temperatures (i don't see where it would get this from).

    The ignition module is just that ignition and safety checks, correct? I am not sure what gas valve I have, but looking on the internet i see some have a sensor, if i happen to have this type would this be what controls the firing rate?

    Just trying to get an understanding of how the system works. Just to buy me some time. If the oh crap fund was bottomless I would be asking questions on a new setup.

  8. #8
    In the trades Dana's Avatar
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    I haven't had time to dig into the manual, but there is no down-side to running it only at low fire unless the return water temp becomes too low when all zones are firing. Most finned water tube boilers are fine with the entering water as cool as ~110-115F, but below that there is excessive condensation on the heat exchangers. (Cast iron boilers shouldn't be run with return water any cooler than 130F for similar reasons.) The return water temp is tweakable with the ball valve on the bypass branch, since that valve controls the ratio of boiler output to return-water entering the boiler.

    Take the time to do some temperature measurements under different operating conditions, make sure the delta-T and return water temps are in the sane- zone.

    Running the system at a slightly higher pressure can reduce kettling, but may create other problems. If it's in the 12psi(lowest pressure when cold) to 20psi (highest operating pressure at temp) range you can probably bump it up 3-5psi, but not more.

  9. #9
    DIY Member BillTheEngineer's Avatar
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    Well after some time of looking at the manual, the wiring diagram and the wiring on the unit itself, I figured how to disable the boiler from firing at the higher rate and the system has been fine and quiet. It seems that the higher (second stage) seems to fire whenever there is a call for heat and the boiler temperature was below 160, the 1st stage fires with a call for heat and goes between 140 and 190. Without a call for heat the boiler goes cold.

    I guess the humming was from the water boiling before it had a chance to go through the boiler. I guess my options would have been to put in more pumping or figure out a way for the water to get up to speed before having the boiler fire at the higher rate. the other option would be to combine zones.

  10. #10
    In the trades Dana's Avatar
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    Sounds like the best band-aid for now, and your net efficiency has probably improved.

    It's still worth figuring it out and having the replacement plan on the shelf before it's an emergency though.

  11. #11
    DIY Junior Member Raspy's Avatar
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    The humming or moaning is caused by low flow or low pressure in the heat exchanger. Those Raypak boilers are not just low mass, they are extremely low mass and famous for moaning.

    Low fire is the best answer for now as long as the output is enough to keep you warm, but it's not a true fix. From a casual look at the photo, I'd say the boiler is oversized.

    You might have a stuck pressure gauge giving you the impression that the pressure is normal at 12-15 psi cold and static. You might also have a buildup of sludge in the system reducing the flow rate. It's common over time.

    If you need to change a pump one of these days, change to a Taco 008 or a Grundfoss 15-58 three speed. Do that first on the loop that causes the moaning. If you do change the pumps, flush the system and double check the pressure with a new gauge. See what comes out when you flush it.

  12. #12
    DIY Member BillTheEngineer's Avatar
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    The pressure is close to accurate. Checked it with another gage and the relief valve opened at 30 PSI by the gage (figured that one out when purging air from the system, after changing the relief valve and the reducing valve). There was a small amount of sediment in the system, not much at all to be concerned about. Since disabling the 2nd stage, the system has been quiet and it has not been cold enough to see if it can keep up under the coldest conditions. Generally the lower level the heat never kicks on and I only really make use of one of the upstair zones at any given time (one zone is bedrooms, the other is living room, dining room and kitchen).

    I don't think heat will be an issue even on the coldest of days, (unless I leave a door or two open). I think the manual said the 1st stage puts out 60 Kbtu, which should be more than enough. Yes the boiler is over sized, I haven't done a heat lose but just from reading on this site what is typical, I am pretty sure the 60 Kbtu is more then I will ever need.

    Additionally the cost for heat and hot water (and cooking) is lower than what I anticipated. I guessed on average of $115 per month year round and I my last bill was just under that. From 10/31/13 to 12/23/13 I used 135 ccf (looking at the last to actual readings on the past two bills). I have only been in the house since July and my last house was similar, but used oil and had the coil in the boiler for hot water. The cost to heat that house was significantly more.

  13. #13
    In the trades Dana's Avatar
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    A typical 1960s vintage 2000' rancher on Long Island with at least storm windows and some insulation updates will usually come in under 35,000BTU/hr for a heat load measured by fuel use, under 50K by I=B=R or Manual-J methods, so it would be surprising if you ever needed the full 60K.

    Wednesty-Saturday you'll probably be hitting the 99% outside design temp a couple of times- that'll be a pretty good test. My predicted low in central MA for Saturday morning is -6F, after a predicted high on Friday of +8F- I think L.I. is going to be on the warmer edge of that front, but still pretty cool, but not arctic-cool. (I'm sure I'll be dreaming of Minnesota on Friday! :-) )

    The per-btu cost of gas is currently running less than 1/4 that of oil in my area. Even low-efficiency gas appliances are a bargain to heat with compared to the very best oil equipment, and I don't see any reasons for that situation to change appreciably in the near (or even fairly far) future. Even at Long Island electricity prices it's cheaper by half to heat with heat pumps than oil burners.

  14. #14
    DIY Member BillTheEngineer's Avatar
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    Well after a little cold snap,I find that the boiler (firing on the first stage only) and baseboard radiators seem to be marginal at keeping the house warm. With an outside temperature of 9, a slight breeze and no sun it take about an hour to raise the temperature a degree. The boiler does cycle off and on, and it's a long on cycle and short off (45 minutes on, 5 off). The cut out temperature is a little over 190 and the cut in looks to be around 140. The boiler goes from 140 to about 175 pretty quickly (5 minutes) then slowly climbs to the cut out temp. This is with all zone calling for heat. The outlet temp seems correct, i checked it with a IR gun, the return temp on the upstair zone was about 35 - 40 degrees less, this is with the inside temp being around 63 degrees. The downstairs zone what an even larger temp drop about 40 to 45, but this is because the down stairs was about 50 degrees.

    It seems like the boiler can keep up, and I am sure if i left the thermostat at the same setting all day and didn't let the temp drop when i wasn't there I would not have noticed. I also know I have some insulation work to do in the attic, its not horrible but there room for improvement and room to cut down on drafts too. I think more radiation would be appropriate.

    In a well designed home and a semi-perfect world how quickly should a house heat up? After seeing how mine is I will just not let the temp drop when I am not there on the really cold days. Adding some additional baseboard radiators is not to much of challenge, in some areas. Would adjusting the aquastat to cut in at a high temp (160?) and out at 200, make much of difference. I also could connect the second stage, but didn't think it was necessary since the boiler was able to raise its temp with just the one stage.

  15. #15
    Retired Defense Industry Engineer jadnashua's Avatar
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    For max efficiency, if the boiler is sized for the load, it may run constantly at its design temperature. It may not have much reserve to bring the house up to temp if you set it back, but is probably capable of keeping it at the set temp. Parking it at a higher temp shouldn't do much about the recovery, and will cost more when it is coasting. Depending on the type of boiler, it may require keeping it above 130 to prevent condensation and ultimately, damage from occurring...just depends on what you have.

    The existing baseboards will provide more heat if the temp is increased, but I don't think bumping it just 10-degrees from 190-200 will make much...190 should be plenty to get the convection cycle working well. The difference is much more dramatic when your supply temperatures are lower (and may not be feasible with your boiler). An actual CI radiator is a much more linear heat source than fintube.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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