HVAC guys can't stop loud gurgling noise in my hot water baseboard heaters

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Pablo210, Jan 25, 2018.

  1. Pablo210

    Pablo210 New Member

    Joined:
    Jan 25, 2018
    Location:
    Massachusetts
    I have a continuing problem with a loud noise in my hot water baseboard heaters. I live in a small ranch house with just two heating zones. Sometimes the noise sounds like water gurgling and other times it sounds like someone is pouring a pitcher of water down a gutter. The noise is loudest in the morning when I turn the house digital thermostats up for the day. Also, the noise is much louder in one zone, the zone where I had new Slantfin baseboard heaters installed in Spring 2017.

    The noise started in December 2017 after a local professional HVAC company replaced two brass Taco zone valve heads near my 2002 oil-fired Utica boiler.

    In January 2018, a technician came out to my house to solve the noise. He replaced the bladder in my boiler's expansion tank, then purged the air out of the system. This did not solve the noise. In fact, the noise actually got louder!

    Later in January 2018, a supervisor came out to my house and concluded that my boiler was operating at too high a temperature, causing water to percolate and producing steam in the system. He recommended replacing my old Honeywell thermostat with a new Honeywell digital aquastat thermostat. The technician did this, then purged the air out of the system. This has somewhat reduced the noise, but it has not stopped it.

    I need to call another HVAC company to get the noise problem resolved, but I would be interested in hearing from anyone on this forum about a theory as to what is causing it. Is one of the new Taco zone valve heads defective? Does one of the valves itself need to be replaced? Is there an air leak somewhere in my system? Is my boiler at the end of its life?

    Any help and insight would be appreciated. Thank you. Pablo
     
  2. plumber69

    plumber69 In the Trades

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    Prince Rupert, British Columbia
    Has to be air. Do you have bleeders on your baseboard? R you pumping towards your expansion tank or away from it
     
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  4. Dana

    Dana In the trades

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    Air in the system is a possibility. There is usually an air purging device on the system near the boiler to get rid of any residual air, but if it's not installed optimally it may not do the job. Any time the system is opened up more air is introduced, but as long as there is enough flow to get heat it should eventually be purged by the air scoops & vents.

    When the system was opened up to replace the expansion tank more air was introduced, and the manual purging was incomplete (as it always is.)

    Whenever the system ends up in a low-pressure condition it can take on air from reverse air flows through the system vents or elsewhere. There could be other reasons why your system isn't auto-purging the last vestiges of air. What does the pressure read at the end of burn, and what is it after a long idle when the boiler is cooler and the pump isn't pumping?

    Most systems are over-pumped, and overpumped systems are inherently noisy even without air (some even have cavitation issues on the pump impellers), but can also take on air due to pressure differences generated by the pump.

    Some pictures of the near-boiler plumbing, including the zone manifold, expansion tank plumbing, and pump arrangement may provide useful insight. Do the baseboards have air bleeders? (Usually under the end cap sheet metal, ideally on the outflow end of the baseboard.)

    The boiler model w/ nameplate BTU information, the pump model number, and the lengths of baseboard (broken down by zone), might also be useful. This might be resolvable with a smart-pump, or maybe not.

    Was the Honeywell that got swapped out an aquastat /boiler-control or was it a thermostat? (The terms aren't interchangeable.) If aquastat or boiler control, model numbers are useful. Even the smallest oil boilers are ridiculously oversized for small ranch houses, and tend to run very inefficiently, well below the nameplate AFUE due to the ultra low duty cycle. If there isn't enough baseboard on each zone it can even short-cycle. It's possible that the Honeywell was a heat-purging controller to help reduce the numbers of burn cycles, lower the standby losses, and lengthen the minimum burn times or it could be something else.
     
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  5. Pablo210

    Pablo210 New Member

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    Location:
    Massachusetts
    I asked the technician about bleeders and was told that my Slantfin baseboards do not have bleeders. I have no idea about the expansion tank, as I'm just a new homeowner and have no experience with HVAC matters.
     
  6. Pablo210

    Pablo210 New Member

    Joined:
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    Location:
    Massachusetts
    Thanks for the lengthy reply, but I'm lost. I'm a new homeowner with no HVAC experience and I'm unfamiliar with most of the terminology you used. I've attached some photos of my boiler set-up and the old thermostat and zone valve head that were replaced. A neighbor said my system has a brass air vent (visible in photo), so he suggested I wait a week to see if the system purges air by itself. At this point I have no other option, as I already owe the HVAC company $$$.
     

    Attached Files:

  7. Dana

    Dana In the trades

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    Location:
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    In your first picture the gray iron block that has the expansion tank (the gray cylinder that looks a bit like a propane tank) hanging off it is an "air scoop". On top of it the bronze thingy with the li'l tire-valve type cap on top is a vent that lets air escape. You'll note there is also another vent directly on top of the boiler.

    In the picture with the nameplate I can see the model number is a Utica SFH3100W, with an input of 140,000 BTU/hr, and and 117,000 BTU/hr output.

    The air-scoop needs at least a foot or so of straight pipe on it's input side to function well It's hard to tell from the angle of the picture how much pipe you have, but it doesn't look like much on either side. It looks to me like there's a ball valve (green handle, bronze body) just before the scoop, and a 90 degree ell just before the ball valve. The ell is introducing a lot of turbulence just as the water enters the air scoop, which keeps the bubbles from separating. It's probably still doing something, but it would do far better if it had a straight run on the intake side of the air scoop. There's usually an arrow on the side indicating the direction of flow:

    [​IMG]

    Ideally the arrow on the air scoop (where the expansion tank is located) would be pointed in the direction of the pump and also be a straight pipe. Looking at the manual it appears the direction is correct from expansion tank to pump, but there's a 90 degree ell introducing turbulence at the pump input. That will make it more prone to cavitation and noise. (What is that pump, a Taco 007, mayhaps?)

    But verify the direction arrow cast into the air scoop body is pointing away from the boiler, and that the flow direction arrow cast into the pump body is pointing away from the air scoop/expansion tank. (You'd be amazed at the kind of stupid-attacks like that still work when the boiler is ridiculously oversized for the load.)

    [​IMG]



    The gauge on the corner of the boiler indicates both temperature and pressure. What is the pressure reading at the end of a burn cycle? What is the pressure reading at the beginning of a burn cycle?

    The last picture shows an aquastat (not a thermostat) and the top of a zone valve. I take it that the gray box to the left of the red burner power switch is what replaced it? Is there a model number on the new one? (Sometimes you have to remove the cover to see the model number.)

    An output of 117,000 BTU/hr is enough heat to keep my 2400' 2x4 framed 1.5 story + 1600' of conditioned basement nice and cozy at an outdoor temperature of -130F (< no, that's not a typo), and probably yours too. If you are on a regular oil fill up service that stamps a "K-factor" on the billing slips, what was the most recent K-factor? It's possible to determine the design heat load of your house and optimal boiler size from wintertime K-factors, but not during the shoulder seasons or summer (due to errors introduced by the water heater zone, and higher solar gain from windows, etc.) If this thing is more than 1.7x oversized for the space heating load (which it almost certainly is), it may be worth investing in a smarter boiler control, if the new Honeywell isn't designed to purge heat from the boiler at the end of a call for heat from the room thermostats.

    At an average water temperature of 170F (180F out of the boiler, 160F coming back) the Slantfin baseboards will deliver about 500BTU/hr per running foot of baseboard into the room. For the boiler to not cycle on/off during an extended call for heat by the zone thermostats (the ones on the wall that you can adjust the room temp with) it takes 117,000/500= 234 feet of baseboard. With less baseboard than that the boiler will cycle on & off between it's low-limit and high limit temperatures determined by the aquastat settings. The less baseboard you have, the more quickly the temperature will slew from the low-limit to the high limit. If that burn time is less than ten minutes the boiler won't hit it's AFUE efficiency numbers, and if it's less than 5 minutes it's going to be substantially less.

    So it matters from a maintenance and efficiency point of view how much baseboard you have. Care to share that info?

    The return pipe enters the boiler near the bottom at the back side, visible as bare copper that's parallel with the exhaust vent pipe in the picture. When both zones are calling for heat (turn both wall thermostats up by 5F), measure the return water temperature with a meat thermometer taped or wired to the that pipe tightly wrapped with an inch or more around the business end of the thermometer. (It can be a foot above the boiler if you like- no need for a contortion act between the boiler & water heater.) If the boiler is cycling (probably is), note the temperature difference between the boiler's gauge and y the end of a burn measure the temperature of the return water, and compare it to the temperature on the boiler's gauge. If it's only 5-10F you can definitely back off on the pumping rate, which will lower the overall turbulence in the system that is keeping the air from separating and self-purging quickly.

    It looks like there are separate ball valves on each zone, located above the water heater, which would be a reasonable spot to start throttling back flow. Unlike gate valves, ball valves can be reasonably operated in a partially open position without excessive wear, and are often used for adjusting flows. When restricting flow, measure the return water temperature on the zone plumbing near the ball valve so that you know when it's being cut back too far. A difference of 15-25F lower than whatever the boiler temperature reading is would be about right when the boiler is at 150F or higher.

    There are smart pumps that work as drop-in replacements that can be programmed to a particular flow, pressure, or even temperature difference (with wired sensors). Whether or not it's worth the hassle is your call, but it'll use about 1/10th the electricity of the existing pump, and will be almost guaranteed to be quieter, even when there is still air in the system. But slower flow/lower turbulence will also give the sub-optimally plumbed air scoop and the boiler vent a better shot at purging the residual air quickly.
     
  8. Dana

    Dana In the trades

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    Location:
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    If you start tweaking the flows and monitoring the temperature differences, bear in mind:

    1: Running an oil fired boiler chronically with returning water that's cooler than 140F can result in corrosive condensation in side the boiler or in the flue piping. It's possible to plumb in a branch to feed some of the boiler output to the boiler input to prevent that, but there doesn't appear to be that sort of bypass branching on your system as-installed.

    2: Also, running it chronically at in-to-out temperature differences of 50F or higher can mechanically stress the boiler, making it more leak prone. A 20-25F temperature difference is a good target range, but 15F or 30F is still fine.

    During a cold-start or when a zone is first calling for heat there will be a period of time when both of those conditions are violated, but as long as it don't persist through a large portion of the burn it's fine.
     
  9. plumber69

    plumber69 In the Trades

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    Location:
    Prince Rupert, British Columbia
    From the looks of it your pumping towards the expansion tank. You should be pumping away from it
     
  10. Dana

    Dana In the trades

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    Jan 14, 2009
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    The supply out of this boiler is straight out the top, the return is in the back or the boiler, at the bottom.If that's a Taco pump, looking at the pump in the orientation the electrical connections would have to be on the left to be installed backward, pumping toward the expansion tank. Note the arrow on this Taco pump, relative to the electrical box:

    [​IMG]

    It's a bit hard to see, but it looks like in Pablo210's installation the electrical box is on the right (obscured by the auto-fill plumbing in the shot), which means it would be (correctly) pumping away from the expansion tank.

    [​IMG]
     
  11. Pablo210

    Pablo210 New Member

    Joined:
    Jan 25, 2018
    Location:
    Massachusetts
    Below are another couple of photos of my boiler, sideviews.

    Even if some of the connections are incorrect, why would my noise problem suddenly start in December? I had the boiler tuned up in mid-October and used it until mid-December without any noise problem. The noise started after the two brass Taco zone valve heads were replaced in mid-December.

    IMG_0310.jpg

    IMG_0309.jpg
     
  12. Dana

    Dana In the trades

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    Jan 14, 2009
    Location:
    01609
    The orientation of the air scoop and pump are correct, but the installation of both are ridiculous. Both need at least a foot of straight pipe coming into the intake side from the last ell, and it's far better for the pump if it's in a straight line from the expansion tank without the intervening ell.

    Q: "Even if some of the connections are incorrect, why would my noise problem suddenly start in December?"

    Answer:

    A: "The noise started after the two brass Taco zone valve heads were replaced in mid-December."

    When they replaced the zone valves the opened up the system, introducing air into the water. The poor installation of the air scoop makes it function less quickly/well than if done by the book. If you run it long enough the air scoop vent and the vent on the boiler will eventually purge the air, provided the rest of it is all up to snuff. Slowing the flow would make that happen faster.

    Still no information to share about system pressure? (It matters- really!)

    How about baseboard lengths (by zone)?

    Burn times?

    Part numbers / model numbers on the old & new aquastats?

    Trying to run a diagnostic with only half the information can be futile.

    The direction arrow on that model pump is probably on the bottom of the pump housing, but it still looks like the correct direction.
    [​IMG]
     
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