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No pressure then pressure

Sgtdng
Sgtdng Member Posts: 19
I have a Noritz Combi boiler cb180dv has been trouble since day 1 but it has done the job. Now for whatever reason the gauges on the system showed zero pressure and the boiler went into fill mode which I don’t have dhw hooked up so it could not fill itself.  I turned the power off since I thought I had a leak but when I went back to it in the morning it had 12 psi on all the gauges now.  I powered the system back on and it ran all day till there was no longer a call for heat. ( I assume since the shop was up to temp the next morning) the next morning the boiler was in error again saying low pressure.  I shut the power off again and watched the gauges for the rest of the day and watched them go from 4 psi to 7 psi by nightfall.  I waited with the system powered off over night and in the next morning the pressure came back up to 12 psi and was able to fire up the boiler.  I checked the psi in the expansion when the system read zero pressure and the tank had 12 psi. Tap test sounded normal water on top and air on bottom.  So I’m at a loss on how a system can go into failure from a low pressure reading, but regain pressure over a night or 2 when the power is off to the boiler.  I can see water and glycol mix expanding with rising air temperature, but the air temp was only dropping. Getting colder in the shop as the system is powered off.  It’s 19 degrees outside and thermostat set to 64 inside the shop.  

Comments

  • HomerJSmith
    HomerJSmith Member Posts: 2,435
    How is it piped? Is this something new or a problem from the beginning?
  • hot_rod
    hot_rod Member Posts: 22,105
    With 0 psi in the system and 12 on the tank pre charge there cannot be water in the expansion tank. The diaphragm would be pushed up against the nipple

    got a pic of the system 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19
    The system has been working during the winter time for the last 4 years with the exception of needing multiple new parts to keep it running.  So this is a new problem.  I get that the diaphragm would be pushed up some but how does that explain the pressure coming back and showing on the gauges after a day or 2?   I know the top of the tank sounded dull and the bottom sounded tingy. 
  • hot_rod
    hot_rod Member Posts: 22,105
    Are the pumps running when you check pressures?
    The pump in the boiler looks like it is pumping at the expansion tank, so the delta p will show up as a drop in pressure.

    Looks like there was an additional pump removed? Recently? Is that when pressure issues showed up?

    The lower gauge looks like it is on a y strainer, if so has it ever been cleaned?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    GGross
  • Sgtdng
    Sgtdng Member Posts: 19
    Noritz told me to remove that pump the first year when I originally installed this system cause the boiler had the pump inside.  Not sure what delta p is but this was the way noritz wanted it.  The system has ran for 4 years till this new problem which just occurred last Friday. I have not pulled that y strainer, and the gauge is shortly after that strainer.  When the pumps fire up the pressure does go up a little bit. Which is normal from what I understand. The system will lose pressure after running for awhile( never when I’m there to watch it) then regain pressure after I shut the power off to the boiler.( takes a day or 2 for the pressure to come back up to the minimum fire amount 8 psi). The boiler is set with a plus/minus 4 psi from 12 .  So when it reaches 8 psi it will try to refill up to 16 psi.  Of course it can’t refill since I don’t have city water in the building. But it will regain its pressure after sitting with the power off.  
  • dko
    dko Member Posts: 586
    Could you take another photo, but facing straight at the wall and no part being cut off (top and bottom of boiler as well- where the neutralizer tank is).

    I see piping from the top of the combi where the the relief valve should be, but you also have one after the air separator.

    Is every pex loop for radiant or do they go into radiators as well?


  • hot_rod
    hot_rod Member Posts: 22,105
    Any way to shut power off, let it sit overnight and check pressure? Does it ever drop to 0 psi? That would be an indication of a leak, or relief valve discharge.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19
    hot_rod said:
    Any way to shut power off, let it sit overnight and check pressure? Does it ever drop to 0 psi? That would be an indication of a leak, or relief valve discharge.
    It gains pressure when the power is off.  The first time this happened the pressure was down close to zero ,may have been 1-2 psi but definitely not above that.  I let it sit overnight with the power off so I could get the thermocam and pump I needed to refill and check for leaks. But the next day after I got everything I needed to check leaks I noticed the pressure was back up to 12 psi.  The system fired up and ran until there was no longer a call for heat some time when I was sleeping.  Never had any relief valve discharge or moisture any where outside of the concrete slab.   Fast forward a few days from then after trying to figure this thing out, I had it running yesterday since the pressure was up, and later at night I went back out to see if it was still running, and it was not.  I checked the pressures and it said 12 psi on all the gauges so I figured it should be fine and start again in the middle of the night when there was a call for heat.  I checked went out this morning and it was in fault again with only 7 psi on the gauges.  So I thought that was wierd. Why would it  go back into fault after it shut off with 12 psi still reading in the system. But start up and some time during the heating cycle loose enough pressure to fault out again. I shut the power off again this morning and I’m willing to bet when I go check again in the morning it will have enough pressure to fire up again.
    I will post another picture if I can find one after I post this message.
  • Sgtdng
    Sgtdng Member Posts: 19
    These are older picture but the best straight forward ones I have. I have built a room around this thing and I can’t stand back far enough to get a bigger shot.  Yes there are 2 blow off valves on this system.  I built the system left of the boiler before I had the boiler and did not know the boiler had one as well.  Thus the reason for the 2 blow off valves.
  • hot_rod
    hot_rod Member Posts: 22,105
    With the power off, no pumps running what is the pressure reading?
    Now fire the boiler up so the pump inside is running,
    I suspect the gauge pressure will drop a few psi. It does this because you are pumping at the expansion tank, instead of away from it. It looks like to me.
    These graphics shows how the pump can either increase or decrease the gauge pressure depending on where the tank connects.

    Maybe you see the pressure decrease when the pumps are running?
    Also when the boiler heats, pressure should increase some.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19

  • Sgtdng
    Sgtdng Member Posts: 19

    This I picture right after I installed the boiler about 4 years ago.  The vertical pump was removed as well as the zone controller since I’m treating this as a single zone.  Maby if I stay here for a few more years, which ain’t likely do to the rising taxes, I will put in a partition for the street rod and control that area as a separate zone.  Other than those couple things I mentioned the only thing that has changed is the condensate drain system I made to have a supply of fresh water to wash my hands when I need to.
  • hot_rod
    hot_rod Member Posts: 22,105
    If the system drops to 1 or 2 psi I would suspect a leak in the slab. I can’t explain how it could go from 1psi to 12 psi without water being added

    The installation manual does show the better location for the expansion tank
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19
    hot_rod said:
    If the system drops to 1 or 2 psi I would suspect a leak in the slab. I can’t explain how it could go from 1psi to 12 psi without water being added The installation manual does show the better location for the expansion tank
    I agree, I can’t explain it either. But something is causing it.  Noritz also said the same about the expansion tank, but it’s been running fine like this for a bit over 4 years now.  Again I built this before I even bought the boiler.  Little better and neater design than my in laws and his tank was on the top like this as well.  His system has been flawless without a single issue for 6 years now.
  • dko
    dko Member Posts: 586
    edited March 2023
    Two options to optimize your piping below. There are better ways, but these will require the least amount of work with the least amount of $ in material and still function. Less than $20 worth of fittings, 4-6 90s, few 45s for offsetting, 0-2 couplings and 2 tees. Probably don't need to even buy another length of pipe, worst case plug the left relief valve tee and use that pipe. one at your boiler is enough.

    Not that this will solve your issue, but first things first?




    Also considered just going straight off the pex manifold return eliminating that loop to the webstone p/s valve and the rest of the return and reattach strainer/gauge with couplings. would be cleaner and not rely on remembering to keep the valve closed.
  • Sgtdng
    Sgtdng Member Posts: 19
    I’m sorry, I didn’t really look at those pictures close before I posted them.  That pump is in the horizontal position and Not the vertical like shown in the picture.
  • Sgtdng
    Sgtdng Member Posts: 19
    Also, how did you change the photos like that?  That’s pretty good!
  • Sgtdng
    Sgtdng Member Posts: 19
    dko said:
    Two options to optimize your piping below. There are better ways, but these will require the least amount of work with the least amount of $ in material and still function. Less than $20 worth of fittings, 4-6 90s, few 45s for offsetting, 0-2 couplings and 2 tees. Probably don't need to even buy another length of pipe, worst case plug the left relief valve tee and use that pipe. one at your boiler is enough. Not that this will solve your issue, but first things first? Also considered just going straight off the pex manifold return eliminating that loop to the webstone p/s valve and the rest of the return and reattach strainer/gauge with couplings. would be cleaner and not rely on remembering to keep the valve closed.
    With having both the inlet and outlet that close to each other, won’t that just cause the boiler to just suck the hot water going into the system before it has a chance to get thru the floor? 

    Once it gets to be summer time and I don’t need heat any more I will rip this thing apart and redo with however you think is best.  I can throw a few hundred at it , but I need reliable heat thru the winter.  Then I can spend more time trying to fix other people’s stuff and keeping food on my table then fixing mine.  I get laid off in the winter and work out of my shop till I get called back in spring.
  • HomerJSmith
    HomerJSmith Member Posts: 2,435
    I think that the pump (Yellow sq) should be moved to the other yellow sq. I like pumping into the highest pressure loss. It seems to me that you are pumping into closely spaced tees. Water is going to flow from the highest pressure to the lowest pressure. I think that the green pump is at the highest pressure and is pushing water thru the tee to the return of the boiler as well as pushing against the supply from the boiler to the tee which can change the pressure differential.
    Where the red star is the highest pressure is going to win. Does this make sense? I'm going to post this, but I'm not sure I'm on the right track.


    Zman
  • Zman
    Zman Member Posts: 7,569

    I think that the pump (Yellow sq) should be moved to the other yellow sq. I like pumping into the highest pressure loss. It seems to me that you are pumping into closely spaced tees. Water is going to flow from the highest pressure to the lowest pressure. I think that the green pump is at the highest pressure and is pushing water thru the tee to the return of the boiler as well as pushing against the supply from the boiler to the tee which can change the pressure differential.
    Where the red star is the highest pressure is going to win. Does this make sense? I'm going to post this, but I'm not sure I'm on the right track.


    That’s exactly what I was thinking!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 22,105
    With. A circuit simulator you could define better what is going on in the closely spaced tees.

    Keep in mind, what goes into a tee must come out of a tee. One of the core teachings in “Pumping Away”

    Assume the lower pump is sized to move 3 gpm for the six loops, 1/2 gallon per.

    So 3 gpm has to go thru that tee, straight across, when that distribution pump is operating. Hydraulic separation is happening, there should be no flow into the boiler loop.

    Now you would calculate the flow from the boiler loop, based on the pressure drop and the circ in the boiler, call it 5 gpm. So 5 gpm goes in one branch, 5 gpm must come out of the other tee branch.

    So if you knew those flows and a few temperatures you could predict the “ blended” temperature to the loops. When both circs are running 8 gpm is moving between the closely spaced tees, at the second tee, 5 must go back to the boiler, 3 must go down to the manifold. What goes into a tee must come out of a tee.

    More complicated is determine how both circs are “seeing” the expansion tank. Looking at it both are pumping at the tank. A gauge on the outlet of both circs, or some calculating would determine those dynamic pressures
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19
    I wish I knew how to do that photo work so I could give you a visual of what I think you’re saying.  But I will try and tell you instead.  So move the horizontal pump to the vertical position, close the excess valve right below where the vertical pump will be, or put the vertical pump below that valve just before the lower manifold, and put both the inlet(hot) and outlet( return) right next to each other in the vertical run where the hot supply line in now.  Would the excess return line just above the upper manifold even need to be there anymore?  Or am I as confused as I think I am.  Maby if you could draw out a complete diagram of how this would be best, I can completely reconstruct the system this summer.   
    I hooked up a fill pump today since the pressure was low again thinking it would go into a full demand as soon as I turned it on, but as my luck usually goes, it turns on and the pumps upped the pressure enough where it didn’t call for a full demand.  The set up I made doesn’t have a pressure switch so I can’t just leave it on overnight when it will call for a fill, so I will need to wait till morning and hope it will need it then.
    I really appreciate all the help from everyone here, and hope I can repay the favor someday.
    please keep the ideas coming.  Thank you.
  • hot_rod
    hot_rod Member Posts: 22,105
    I doubt a repipe will fix the fact that the system pressure drops that much, from 12 to 4 or 0 psi?
    You mentioned 0, 4, 7 psi with power off?
    I’d pressure test the radiant manifold and loops first.

    The piping is not ideal, especially for air removal, but it sounds like it has heated for 4 years?
    Piped like your March 14 pic currently? It should heat. The loops can circulate, and the boiler can inject heat. Assuming both are spinning🤔
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,285
    Hi, I'm a simplistic thinker, but in thinking about pressure very slowly coming back up, I'm wondering if there are any check valves, plugged strainer, back-flow preventers, or such anywhere in the system that could leak pressure slowly back so the gauge sees it. Mysterious things generally mean that we don't understand all of the forces at play.

    Yours, Larry
    ryanwcHomerJSmith
  • hot_rod
    hot_rod Member Posts: 22,105
    What have you changed or tried since you started the thread? Did you check the Y strainer as suggested?

    My process without buying or changing anything.

    Turn off power and gas. Hold open the relief valve drop pressure to 0

    Check the expansion tank pressure, adjust if necessary to 10 psi with an air pump

    Remove the strainer, put it back together without the screen

    Tighten the caps on any air vents

    Fill the system to 10 psi, purge at the relief.

    Let it set, power still off, come back in a few hours, overnight if possible

    See if the pressure has dropped at all. It could actually go up if you refilled with cold water, just by warming to ambient.

    If it has dropped with the system completely closed off, look for the leak.

    You have valves on both manifolds so you could pressure test that assembly. A short wash machine hose would allow you to hook a garden hose to the manifold valve. A hose type pressure gauge on the opposite manifold valve, take it up to whatever your house pressure is, or use a pump if you do not have water out there.

    If everything holds pressure 10 psi in the boiler piping 50 or so in the Pex loops, then decide which piping changes you want to make.

    I’d add an Axiom fill tank also as it will burp air when you re-fire it again, cheap insurance against low pressure lock outs. If you have glycol it can take days to get all the air eliminated.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Sgtdng
    Sgtdng Member Posts: 19

    I rigged up a refill system and allowed the boiler to refill the system to its tolerance. Closed the ball valve for the refill system after it was completed. I let the whole system sit with out power for 2 days and it still had the 16 psi it pumped it up to. Once I shut this system down for the summer I will redo the main loop design.