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Unplausable causation

Nick333
Nick333 Member Posts: 14
I am a super of 24 years in a 440 unit coop on the upper East side,I have 3 federal boilers original to the building with newer dual fuel IC burners running natural gas/#2 oil, the past couple of weeks I have been getting hot water in the cold water lines of 2 apartments closest to the boiler room when 1 of the 3 boilers fails out on flame failure, the building is 21 stories tall and takes up the whole block from street to street, I have 2 Holby mixing valves in front of the middle boiler which I call boiler #2, my cold water main comes from the left and has a cold water loop that splits off to feed the dual coils of each boiler, the remaining main continues along past boiler #1 to in front of boiler #2 where there is a tee that comes off to feed the 2 inlets of the mixing valves, then continues on towards boiler #3 where above it is one of the apartment lines that is being affected and it feeds the cold water to the kitchens and bathrooms for 17 stories.

There is a iron body check valve after the cold water tee and before the mixing valves, that check valve is supposed to stop the mixing valve water from going backwards into the cold water main which I understand and which makes sense, NOW HERES THE UNPLAUSIBLE PART, if that check valve was bad I guess it would allow water to back flow through it causing hot water in the cold water lines closest to the boilers all the time, if the check valve is not bad the hot water should not be able to back flow at any time, how or why is it if one of the boilers fails overnight, in the morning they have hot water in the cold water lines and when I reset the boiler and get it running again the problem resolves itself.

I have gone over this with my building plumber, building engineer and boiler company and all of them think I’m crazy when I tell them the cause is the boiler failure somehow, is it possible that when a boiler goes off line and cools down that water passing through the coils can cool and create a vacuum inside a closed system and actually start pulling on the check valve and allow the hot water from the hot water side of the mixing valve to back flow through the check into the cold main, everyone says no but there is nothing that changes to water flow or pressure in the system just because 1 boiler is not running at the time, the water is still traveling through the coils, the cold main still has the same water pressure, if anything you would imagine that if the boiler failed the hot water in the building would not be as hot as it should, it’s like a bizarre backwards universe I’m in.

Sorry for the long winded post

Comments

  • SweatyInToronto
    SweatyInToronto Member Posts: 73
    There's that old saw about eliminating all possibilities until the remaining one, no matter how unplausible, must be the correct explanation, right?

    That said, is resolving the boiler failure first feasible?
  • Jamie Hall
    Jamie Hall Member Posts: 16,329
    edited July 23
    I think the first thing I'd do is to to take Boiler #2 off line completely and close all the manual valves leading to it from anything and see what happens.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Nick333
    Nick333 Member Posts: 14
    I try my best to keep my mechanical equipment running at peak condition, I am anal about it, but it is still mechanical equipment and its bound to have issues every now and then which is normal, my bigger concern is not being able to diagnose the underlying condition because what should make sense doesn't in this case, I still have no plausible explanation as to why in a closed system with 2 other boilers running it would happen when the 1 fails
  • Nick333
    Nick333 Member Posts: 14
    I could isolate that boiler but that would still leave me with the other 2 boilers, do I wait for #3 to fail at that point to see if the problem reoccurs,  then what, the problem happens when #2 or #3 fail 
  • mattmia2
    mattmia2 Member Posts: 3,441
    How long does this hot water in the cold last? Is it continuous or is it intermittent? I'm thinking some section of cold water pipe gets heated through conduction from some piece of heating pipe that only gets heated when the failing boiler is ofline.
  • Nick333
    Nick333 Member Posts: 14
    The hot water in the cold water lines will continue until I reset the failed boiler, once the boiler reaches aquastat temperature it goes away, it couldn't be convection because it is traveling from the boiler room up 17 stories of apartments with 2 bathrooms and a kitchen, if you run the water on the 12th floor for instance it will just het hotter and hotter
  • ratio
    ratio Member Posts: 2,822
    What does the aquastat control? Another pump?

    I think you should try what @Jamie Hall suggested above, start closing valves & see what changes.

    How far out are repairs to the #2 boiler?

    The only time I've had a similar issue (hot water backfeeding into the cold), it ended up being a shutoff gate valve that dropped the gate off the stem & forced water to feed back through a hot-cold hand sprayer valve that had both valves open. If you can fund out where exactly the crossover is occurring, that's a major clue to what's happening. An IR camera is a good investment. I have a Fluke VT04 & a FLIR One Pro. I can't recommend the FLIR enough.

  • Nick333
    Nick333 Member Posts: 14
    The aquastat keeps the boiler temperature at 180 during the summer to make hot water for the whole building,  in the winter the boilers run off the pressuretrols on the steam header, #2 boiler and #3  boiler are operational, if I get a failure i can probably get it operational again in a few hours during the day,  its when one of them fails in the middle of the night and I dont get to it till morning that the whole line of apartments is having the issue. I understand your explanation about the gate valve, same as a washing machine hooked up to hot and cold and check valve fails or single handle shower bodies with bas check valves,  could let water pass from hot side into cold side, my issue is larger than that because I can figure out where the source is coming from, the boiler coils are feeding into 1 side of the mixing valve and the cold water main is feeding into the other side of the mixing valve, im no getting any pressure drop on the cold water side that would allow the hot water to force its way back, but it will happen when 1 of the boilers fails and cools down. then the hot water from the coils forces its way backwards through the mixing valves, a swing check and dumps into the cold main and when someone upstairs in the affected lines opens up their faucet in the kitchen or bathroom it starts filling the entire 17 stories, I know I have to start at the check valve because that should not let water pass backwards,  the problem with that is the check appears to be working when the boilers are working and failing when 1 boiler fails, they are 2 seperate things. how is it possible for a cooling down boiler to create enough suction to pull open a check valve of that size with all the pressure of a 21 story building gravity pushing on that check to keep it in the closed position,  if the check was bad I would have the problem continously ever day, if the check is working then it wouldn't matter if the boilers were off or on, it has kept me guessing the last couple of days and I appreciate the responses
  • Nick333
    Nick333 Member Posts: 14

  • dopey27177
    dopey27177 Member Posts: 680
    Because this affects 2 apartments, I have this question.
    Do the showers in each apartment have extended shower heads where at the shower head there is a valve to stop or restrict water flow while the shower body valve or valves are open causing a cross over of hot water into the cold water piping.

    Many people forget that the hot water line water pressure is slightly greater than the cold water pressure, that why new shower bodies came with a built in check valve or a sliding bar to equalize water pressure within the shower body and prevent crossover.

    Jake
    mattmia2
  • mattmia2
    mattmia2 Member Posts: 3,441
    Is there a recirculation or even booster pump for the dhw that is somehow tied to the failing boiler's controls?
  • Nick333
    Nick333 Member Posts: 14
    Thanks Jake, its affecting the whole line of bathrooms and kitchens, 16 kitchens and 32 bathrooms, I have had similar less broad issues in the past in different apartment lines where people install seperate hot and cold water controls and seperate shower head, tub spout and hand held showers fixtures and they turn on the hot and cold water and then just turn off which ever head they are using and cause the hot to push into the cold since the hot water is circulated and has more pressure upstairs,  that I van find easily because its local and affect only the apartments above where that passing is occurring, im actually experiencing a full on draw backwards through a check valve when 1 boiler fails or is taken off line which I cannot find a answer for 
  • Zman
    Zman Member Posts: 6,714
    Any chance you could sketch it out?
    Have you tried turning off the boiler and feeling the pipes to see where the hot water is entering the cold pipe?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
    PC7060
  • Intplm.
    Intplm. Member Posts: 1,328
    Those dreaded cross-connections.
    @Nick333 here is some plausible causation that might be the issue and it could be this simple...
    Look to find a hose connection wye adapter on a sink or laundry or elsewhere that is hooked up to both cold and hot water. There might be your answer. I say this because I too have been in this situation and after a couple of times going through all of this troubleshooting, it was someone who put, and keeps putting on a hose-type wye fitting.
    Good luck and I hope that this helps.
  • Nick333
    Nick333 Member Posts: 14
    Thank you Zman,I determined that the water is backing in from the mixing valves where the cold supply feeds into them, once it gets in there its flowing back past the check valve which then let's it dump into the cold water main, whats driving me insane is why does this happen only when 1 of the boilers fails or I manually shut one down, nothing changes or gets turned off if the boiler fails except the burner which causes that boiler to cool off
  • Nick333
    Nick333 Member Posts: 14
    Thank you Intplm,  that does make sense on a smaller scale which I have had in the past but that would be local, it couldn't overcome 17 stories of bathrooms and kitchens in such a short amount of time, its definitely coming from the check and mixing valves, that much I have nailed down, my annual roof tank cleaning is this coming Wednesday,  at that time I asked my plumber to try and find a replacement check valve to replace the one that's there, keeping my fingers crossed that it solves the issue,  if not im done, im going to have to run a 2 inch line from the cold main in the laundry room and run it through the boiler room to pipe it into the 2 affected lines and disconnect the original feeds from the main in the boiler room, will post results here, fingers crossed lol
  • Nick333
    Nick333 Member Posts: 14
    Thanks Mattmia, the circulation pumps are not controlled by the boiler,they have manual switches, they run 24-7 to keep the hot water moving
  • Zman
    Zman Member Posts: 6,714
    Do you have a bad check valve?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,188
    I am far from being an expert on this thread. My expertise is in oil heat on residential equipment. That said...

    It comes to mind that a mixing valve may be allowing hot water to pass in reverse in some fashion. without the piping diagram I can't be sure. But logic dictates that when a boiler is down, there is no hot water feeding the Hot inlet of that particular valve. As there is no Hot water feeding that mixing valve, the valve will be full open to the Hot inlet. The cold inlet of that valve will be completely closed. Could this somehow be directing the hot water from the operating boiler(s) water jackets into the cold main of those problem apartments. I'm thinking of domestic recirc pumps may be helping the hot water go where it is not designed to go when the rare occasion of boiler #2 failure.

    The design may be flawed from its inception, but never noticed until the failures became more frequent.

    The IR camera will help diagnose this. especially if you have arrows on your pipes telling the water which way to go. As @DanHolohan says. "...if you don't put the arrows on the inside of the pipe, the water can't see them and may go the wrong way."

    Respectfully submitted
    Mr.Ed
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
    mattmia2
  • Nick333
    Nick333 Member Posts: 14
    Lol, thanks Mr.Ed, I changed the 4 inch check valve today during my roof tank cleaning, im going to put pictures and I hope this solves my backflow problem even though the actual cause that I can't figure out will still intrigue me 
  • Nick333
    Nick333 Member Posts: 14
    Zman, thats what im thinking since its an iron body check valve and it looks original, I had it replaced today, attaching pics now
  • Nick333
    Nick333 Member Posts: 14

  • neilc
    neilc Member Posts: 1,319
    carbuncles
    Nick333