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Pressure drop/combi boiler

andymarandymar Posts: 17Member
I recently installed the Weil Mclain Aquabalance WMB 120 gas combi boiler. The issue I have is the dropping of pressure at idle times. When the system runs, it does so a 20psi. When the unit sits idle for a few hours the pressure gauge on the unit drops to near 4 psi. At 8 psi I get a low pressure fault code and the unit will not supply domestic hot water. When there is a demand for heat, the gauge pops up to 20 psi and unit begins to operate, DHW operates. There is no obvious signs, water leakage, in the system. The system, located on the first floor (720 sq. ft.), consists of two loops, first floor, second floor. Two zone valves, one Taco 007, one expansion tank, one spirovent and one Watts water pressure feed valve (15 psi). 3/4 inch oxygen barrier PVC and slant fin baseboard. The unit is set to operate at a high of 158 degrees. Can anyone explain this? I would assume, that if there was a leak, my system would only be filling to 15 psi, limit of water feed.

Comments

  • DZoroDZoro Posts: 482Member
    Could be a bad pressure tank, improper piping, or combination of both. Remove the tank and check the air pressure. Should be at 12psi when removed from the system. Post a picture of the system.
  • hot rod_7hot rod_7 Posts: 9,030Member
    If you check and set the expansion tank to 15 psi then fill the boiler to 1( and let it sit for an hour, does the pressure drop?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • andymarandymar Posts: 17Member


    This pic should post. Question. If I isolate (turn valve off to) the expansion tank and pressure holds, would that indicate a bad tank.
  • andymarandymar Posts: 17Member
    OK. So I believe I answered my own question. After isolating the expansion tank, the pressure gauge on the unit continued to drop from 13 psi to 10 psi over 30 minutes. Upon opening the valve from the tank, the psi remains at 10, unmoved. My confusion is that: If there was a leak in the system, wouldn't the psi be at 15 psi, the rating of my fee water pressure regulator?
  • hot rod_7hot rod_7 Posts: 9,030Member
    Was the feed valve open or closed during the pressure test?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • andymarandymar Posts: 17Member
    Hot rod. I left the feed valve open.
  • DZoroDZoro Posts: 482Member
    Has 100% of the air been purged from the entire system? Full flush? Why is there a tee to the right of the pump? Is that a boiler or a water heater or combi? Post a pic including the boiler lower piping.
  • hot rod_7hot rod_7 Posts: 9,030Member
    Is the circulator pumping into the boiler, so zone valves on returns?

    If you turn the fill valve off does the system pressure drop to ?

    The fill valve may have a range of pressure from the set pressure, 15? dropping maybe 2-3 psi and start filling again
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • andymarandymar Posts: 17Member
    Hot Rod- The circulator is pumping supply away from boiler. The zone valve are just past the circulator on the supply side. I will turn fill valve off in the am and let you know. Thanks
  • EBEBRATT-EdEBEBRATT-Ed Posts: 4,499Member
    sounds like an expansion tank issue if you have no leak
  • DZoroDZoro Posts: 482Member
    Your pressure tank and fill assembly are seeing the positive pressure of your pump when it is on. The boiler is seeing the reverse effect/low pressure when the pump is on. Need to move the pump or the tank fill, so you are pumping away from the tank and fill.
  • hot rod_7hot rod_7 Posts: 9,030Member
    If the Green circulator is pumping away from the boiler, then the expansion tank is not in the correct location.

    Typically that type of boiler is piped as primary secondary as show in the installation drawings.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • andymarandymar Posts: 17Member
    Both DZoro and HotRod, I do understand and see how this should be re-piped. On Friday I totally isolated the boiler by shutting off valves. The gauge continued to drop pressure on the unit, how, I don't really understand, perhaps a faulty gauge? At that point there was a short period when the gauge did hold at 15 psi for a day or so. he unit is back to losing pressure and has now developed a rumbling, gurgling sound that lasts for about 10-15 seconds when the DHW is called for. The unit then supplies DHW quietly. Any ideas what this issue may be? Related?
  • lchmblchmb Posts: 2,846Member
    simple on the repipe..put your circ where your airscoop is an vice versa. You need to pump away from the point of no pressure change.. which is your expansion, fast fill combo
  • DZoroDZoro Posts: 482Member
    Yes until you move the tank to the other side of the pump you will experience pressure changes and issues. Hard to tell in your picture but there maybe a easy place to put the tank and fill under or close to the boiler. Post a different angle of the boiler for us.

    The rumbling though is another issue and it is usually on the gas side of the equation. That unit MUST BE set up with a flue analyzer. There are no exceptions with this type of a system. Have your technician leave a copy of his results inside the unit. It should have the following percentages CO, O2, CO2, flame current, and outdoor temperature(would be nice), all of these numbers should be within the manufacturers specs. in your installation manual.


  • hot rod_7hot rod_7 Posts: 9,030Member
    Are you contemplating a repipe?

    I think a lot, maybe all your problems may go away if you pipe it properly.

    Any high pressure drop boiler, or heater needs to have the circulator pumping into it and away from the expansion tank. Doing so add circulator delta P to the heat exchanger, raising pressure and usually taking care of rumbling that could be caused by lack of flow and pressure in the HX. Air will be handled also with a proper piping. The noise could be air that is not getting completely evacuated, and could be the cause of the bouncing pressure.

    You have incorrect piping issues, pumping away from the HX and at the expansion tank, a double whammy, I like to call it.

    If the pressure never drops to zero you don't have a leak, changing the hydraulic characteristics I predict will solve your issues.

    Be sure the circulator is sized correctly, and maybe add an additional pressure gauge. Install a 30 psi gauge near the expansion tank connection, the PONPC, point of no pressure change.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • andymarandymar Posts: 17Member
    @hotrod , @DZoro , and @lchmb . I can't that you all enough for taking the time in helping me with my dilemma. Thank you @hotrod , for explaining to me how and why my situation existed. With that knowledge I was able to persuade my plumber to replumb his work, reluctantly I may say. IT WORKED. My pressure now holds at 18 psi throughout all phases. He basically swapped the pump with the tank, feeder valve and air separator hook up. He also moved, by recommendation from Weil, the primary/secondary connection to basically right beneath the unit , from supply to return ports. I do still have a persistent gurgling/rumbling on initial demand for DHW. It will usually stop after a few seconds. I do get hot water. It has, in the past flashed a d3 fault then returns back to suppling hot water. If it continues I will post what manual says may be the cause. It basically says 1- check proper fuel supply,2-remobe/check ignitor for proper gap 3- insure condensate draining properly, 4-Insure venting size and length are correct and unobstructed. Also how do I publicly thank you all on this site?
  • DZoroDZoro Posts: 482Member
    Nice, can you post a new picture? Did he leave you his combustion analysis results?
  • andymarandymar Posts: 17Member
  • andymarandymar Posts: 17Member
    @DZoro, no he did not have the instrument to do the analysis.
  • DZoroDZoro Posts: 482Member
    Combustion analysis is like a health report for your boiler. Its growls and groans are not right, d3 code is telling us its health is not quite right. It may work, but cancer is there and needs to be addressed.
    Strongly suggest finding a contractor who can do a combustion analysis for you. Compare that analysis with the IO manual and keep a report inside or with the boiler for future reference.
    You got the water side in good shape, now to get the gas side in shape.
  • andymarandymar Posts: 17Member

    @DZoro and @hotrod. While I have you both, or others on the line can you look at this photo and see if there is anything obvious in my vent/air piping that may be causing the rumbling, moaning, growling when the boiler fires up. As you can see I used a 3 inch to 2 inch reducer directly after the supplied boiler adapter (grey). I then proceeded with two inch to the roof, total of about 30 feet. Should I have gone away from the boiler a longer distance with the 3 inch pipe? I could probably re-pipe the vent and or fresh air pipe to get another six to eight inches of 3 inch pipe. I plan on having a tech analyze the unit but want to be sure all other issues are completed before hand. Tkx
  • hot rod_7hot rod_7 Posts: 9,030Member
    The installation manual has a lot if requirements for venting. Add all the fittings and pipe length to get the "developed length" see if it matches the venting table in the manual.

    Some noises are from the water side, tiny bubbles or peculation in the HX, some are from the burner side, tough to say without being there.

    A combustion analysis is a must, and may address the noise.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • DZoroDZoro Posts: 482Member
    Check your owners manual, not all allow you to reduce pipe size, also depends on number of elbows and feet of pipe. All the piping should be sloping toward the boiler and proper termination separation is also important.
  • andymarandymar Posts: 17Member
    @Dzoro and @hot rod_7 . Just and update. I did have a combustion tests done and the lower mode on the unit did need an adjustment. More importantly , the banging, gurgling sound appears to have been caused by a slight depression, or lack of pitch, in a horizontal venting pipe nearer the terminal end. Apparently even a slightest amount of water, condensate, lying in the 2 inch pipe was enough for the exhaust to spew it about the piping, thus gurgle sound. Thanks for all your help.
  • DZoroDZoro Posts: 482Member
    Thanks for the report back! Yes the slope back to the boiler is very important=especially when minimal sizing has been done. What combustion numbers did they leave you? High and low fire#'s?
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