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Baffled By Boiler pressure loss

I'm fairly baffled by some issues with our boiler and the water that is coming up via a cracked slab. I'll try to describe this In detail in hopes someone has an idea of what could be going on. It's an old Ako-matic gas boiler. It's a residential home on a slab. We have radiant heat. We recently noticed (within the last 5 months) an indentation on our pergo floor. Since our boiler guy (who has serviced it for the last 7 years) serviced it in October, the spot has grown. When he serviced it, he noticed that the pressure gauge on the boiler itself read zero pressure. He flushed it and filled it and it seemed ok. A few days later, pressure dropped to under 4 (should be between 10-12 lbs). At any rate, he's had to fill it twice and the last time, he filled it to about 20 lbs and said to watch it. It's been at 20, then 10, then 14, then 6 then 14 again to about 3 pounds at the lowest but the heats been fine. Then just after Christmas, I stepped on the pergo and water gushed up and the warped laminate was growing out of control, all in a day. Contracter pulled up laminate and padding was soaked but no water anywhere on slab. However, there is a long crack in the slab. Since then there has been no water coming up. We had rain today but just sprinkling and behold! Water was coming out of the crack. The contractor thinks it's water coming in because of the way water stands next to the house and I was inclined to believe him but I checked the pressure on the boiler as the water was slowly coming up through the crack in the slab and it sat at 3 pounds of pressure where it was 10 the day before. I can understand if there's a call for heat and water starts coming up because it's being circulated-there could be a crack in the pipe. But how could water come up when there's no call for heat and it's been sitting idle? Since it loses pressure when no call for heat after a day or 2, the water has got to go somewhere so maybe it is the boiler after all? We also had a guy come out with a thermal imaging camera to look at all the pipes underneath the concrete and he could not detect a leak. He said that doesn't necessarily mean you don't have one. all he saw was the red from the water underneath the slab. my problem is I don't want to tear up the concrete if it indeed is something from the drainage and the outside but it's ironic that the boilers loses pressure when it sits idle and that's when the water seems to come up as well. i'm inclined to take the hose to the outside of the house and just saturate it to see if it comes through that way. Anybody ever run into a boiler leak when sitting idle but pressure raises and seems fine when there is a call for heat? Thanks much


  • lchmb
    lchmb Member Posts: 2,997
    edited January 2017
    How about some pictures of your boiler and piping? Pressure can increase as the temperature of the water increases. Is the water feed to the boiler on or off as it set's cold? If you have multiple zone's, close off the one in question (supply and return) turn down the t-stat. Set the boiler pressure and see if it changes. Then turn on the zone in question and see if it changes...
    EBEBRATT-Ed Member Posts: 13,790
    Disconnect the boiler supply and return piping. Cap the return and pressureize the supply with air to 50psi. Make sure any components that would be damaged by the higher pressure are removed from the system (like the boiler, circulating pumps etc.) and see if the system holds pressure. make sure that the flowcheck valve(s) are in the open position

    Right now the system is loosing pressure. It's going somewhere.

    the system has pressure on it weather the heat is running or not. The system circulator pump will make no difference.

    I would prepare to do some digging
  • Jamie Hall
    Jamie Hall Member Posts: 21,536
    You have a leak. If you didn't, the boiler wouldn't lose pressure. That's not to say that you don't also have a problem with groundwater coming up through that crack. Indeed, it may be that the crack was caused by groundwater. But I wouldn't be at all surprised if that crack also damaged a pipe in the floor; I'd be more surprised if it hadn't.

    Address both problems -- the leak and the groundwater -- before you even think about repairing the slab and replacing the floor.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • BPH
    BPH Member Posts: 39
    You didn't mention if the expansion tank or relief was checked. Just the system kept losing pressure.
  • BPH
    BPH Member Posts: 39
    Do you have a pressure reducing valve on the system?
  • baffledagain
    baffledagain Member Posts: 3
    I'll add some photos of the system. I'm going to contact the boiler/HVAC guy to make sure the expansion tank was checked but I believe it was. I think he didn't want to put that much pressure on the system but he didn't mention disconnecting the circulator pump. Jamie, I hadn't thought about the crack coming first causing a pipe issue later. That makes sense. Sounds like I'm going to have to tear up concrete to see the issue but it's odd the thermal camera didn't detect a leak. He did see some sort of rectangular plate underneath the concrete but can't imaging they would have put any access valves under the concrete.
  • baffledagain
    baffledagain Member Posts: 3
    Another thing that's strange is when I noticed the water coming up through the crack and checked the boiler was around 3 lbs pressure, I turned up the thermostat so the system kicked on and called for heat. I left for 30 minutes and when I came back, the area was bone dry.
  • BPH
    BPH Member Posts: 39
    kiss...don't jump to conclusions to quickly!!
  • Zman
    Zman Member Posts: 7,467
    Your pressure and temp correlation would indicate a problem with the expansion tank.
    The water coming from the crack seems like an unlikely coincidence.
    I would go with the pressure test if you have the means. Food coloring in the boiler water would also give you something definitive.
    I am puzzled that the IR cam did not pinpoint it. Did you run the boiler hot while testing?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Gordy
    Gordy Member Posts: 9,537
    edited January 2017
    My money is a combination of x tank issue, and a leak. The leak probably gets worse as pipes get warmed up, or even cool down depending on the pipe failure. If he did a system flush (purge) on the piping could have made it worse.

    The only sure way to know is pressure testing as mentioned. If you have not had ground water issues before I'd rule it out.

    Edit: I see an alternative pressure gauge in the back corner. Gauge check. Also see the relief valve was extended out with a new nipple. However the relief valve does not appear to be new. Is it possible the relief valve is weeping .

    Again is the water feeder valve open, or closed at all times. If open it looks quite old, and could be sticky trying to fill on pressure loss. This would still indicate a leak of water, or air removal in the system.

    Is the wall in the pic with the crack in the floor an exterior wall, or interior? If exterior that would be pretty close to the wall to run pipe, but anything is possible.
  • hot_rod
    hot_rod Member Posts: 19,881
    Is it a sell or copper tube radiant system? Judging by the age of the boiler.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream