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Thread: Have some issues with hot water boiler system

  1. #1

    Default Have some issues with hot water boiler system

    Could use some advice on how to fix or find the problem I'm having with my hot water heater system. I'll give a little background and i'll try not to go on too long. For the last couple year I have had water discharging from the pressure relief valve in the system. I used to just let it fill in a bucket and dump it every couple days. Last summer I decided to try to empty the expansion tank. Turns out the valve to isolate it would not close completely. I had a plumber come in close that tank off and attach a bladder expansion tank. Thought that would solve the problem but still have water discharging. I have a contract with a company to service anything with the boiler. They came by last night and I showed them how the bucket was filling up under the pressure relief valve. They disconnected the new expansion tank and tested the psi. It was 12 so that is working fine. They said it may be the pressure reducing valve letting water in slowly. So he shut off the main water supply and told me to call back if water was coming out. When he left the PSI were at 24 since the boiler was fired up. When I checked it this morning it was at 8 PSI. I turned on the main supply got it up to 12 PSI. Bled the radiators upstairs got all the air out and had to put more water in to get it up to 12psi. Now with the main water supply off at 10am it was at 12psi and when I got back at 12pm it was at 10psi. Do I have a leak? I don't see water anywhere. I've attached some pics below of the system. What would cause it to discharge water if I'm losing pressure with the main water supply off


    Thanks Jay

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  2. #2
    In the trades Dana's Avatar
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    A 2psi difference at different operating points and different time of day isn't much of a concern, since the system volume will vary by temperature, and the pressure will also vary by that much between pump-on and pump-off states. But if it continues to drop even with the fill-valve fully off, you have a leak somewhere.

    If the new expansion tank was sized correctly for your full system volume the t & p valve shouldn't continue to spit with the fill valve fully off. If the expansion tank undersized for the system it could still test fine at 12psi, but could still see overpressure at the system high-temp.

    Bleeding/defective autofill valves that slowly bring the system pressure toward your street water pressure are a common culprit for chronic over-pressure issues. Auto-fill valves aren't really all that useful, and seem to cause as many problems as they solve. Filling/pressurizing the system manually then turning the fill valve fully off and checking it at the beginning of the heating season, or whenever the system complains is generally OK. If the pressure drops low enough you'll hear the boiler complaining with some sizzle rumble & bang due to the micro-boil on the heat exchanger plates becoming more macro than micro, and it'll be pretty loud long before there's any hazard condition or damage.

    If that boiler is 40+ years old (and it looks like it might be), the economics of replacing it with something right-sized and higher efficiency might be favorable. Even if it's in pretty good shape it's probably not getting better than 75% efficiency, and it could easily be under 65%. A high-efficiency boiler would get at least 90%, but you'd not be able to vent it into the old flue, and the water heater would also have to go, since by itself it doesn't put out enough heat to keep the flue drafting, and would have guaranteed flue condensation issue plus potential back-drafting issues.

  3. #3

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    Thanks for the reply Dana. The fill valve has only been completely shut off starting last night. No water has been discharged but it has only been one day. I will keep my eye on that. I will also keep my eye on the psi to see if they keep going down. The 2psi difference was just to illustrate that nothing changed and it went down. The boiler did not cycle and the temperature gauge on it did not change. Nothing really changed. The temperatures on the boiler was the same it just dropped from 12psi to 10psi. Once the system is at 12 psi with the fill valve closed it should never really go below 12psi right? I filled it back up to 12psi at 12pm and now at 2:15 its at 11.

    Also what should the PSI be at when the boiler is running. I've read it should be steady around 20. I remember it always being aroudn 24-25.

    Lastly I'm curious what a new boiler would go for? You are correct about it being 40+ years old. It is the original boiler from when the house was built in 1955. So it is actually 57-58 years old.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    A new boiler can be anywhere from a few thousand to over $10K. A nice mod-con would likely be around $10, but NYC with the taxes and cost of living probably more. The pressure will change with the overall system water temp, not just that at the boiler since the water in the pipes to the radiators will cool, lowering the volume, lowering the pressure. Normal operating pressure unless you have a very tall building is typically around 15psi. If the expansion tank is sized properly, the pressure won't change much, maybe a couple of pounds except maybe the first time you fire it up from cold.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #5

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    Thanks for the reply Jadnashua. This is a two family house. I've read online that 12psi is a good number for a two family house. At 12psi all the radiators on the second floor have water to them with no air. The whole day the boiler has not fired on since early this morning. The suns been out and kept the house at 70, the thermostat is set for 68. Throughout the day I have been manually adding water with the fill valve to keep the pressure at 12psi. But throughout the day the temperature of the water on the gauge has been going down. I"m attributing the decline in pressure due to the temp going down. It started at 130 and is now down to 100 degrees. I've filled the system back up to 12psi and will see what happens overnight and when it kicks on in the morning.

    As far as a new boiler I'll have to think about it. I'd like to get this one working 100 percent first. I do like the sound of 90 percent efficient vs 65-70%.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    A well sized, properly setup (that's asking a lot, but possible), a mod-con can approach the high 90's in efficiency. Average would be lower than that, but it's possible to get to the high 90's under some conditions. That will NOT happen if the thing is oversized or not setup properly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7

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    Update- This morning when I check the boiler it had ran to heat up the house. It temp was 160, pressure was 22psi and there was water discharged from the pressure relief valve. The fill valve was shut off.
    With the fill valve shut off we know the pressure reducing valve is not the problem (not letting water slowly in). A professional licensed plumber installed the expansion tank. I know it is in working order, I am not positive it is sized right.
    My questions are
    1)How do I determine if the expansion tank is the correct size?
    2)How do I determine if the relief valve is working correctly and not discharging water at say 25psi?
    3)Assuming the expansion tank is the right size, the relief valve is working correctly and the reducing valve is not in the picture what could be causing this discharge of water. Why is the system getting up to 30psi?

    I will have to wait for the system to cool to see what the pressure is when the boiler has not been working. I assume the pressure will be below 12psi since exactly 2 cups of water were discharged from the system. I can call the my warranty service to fix something but I'm not sure whats wrong.

    Thanks for any help
    Jay

  8. #8
    In the trades Dana's Avatar
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    A system pressure of 12psi is fine for any 1-2 story house. In taller houses it make take higher pressures to keep sufficient pressure on the system on the upper floors.

    If the system was brought up to 12psi when the average water temp in the system was >130F it might be as low as 10psi cold, but not any lower.

    To determine the minimum size for the expansion tank the total system volume has to be added up, including the volume in the boiler + radiators + plumbing. Then the difference in water volume has to be calculated between the room temp and the peak operating temperature of the system. The volume of 180F water is larger than 140F water, which is quite a bit bigger than 70F water, when the system is off. The expansion tank needs to be sized to handle the difference in volume between room-temp and the average water temp at the highest operating temp. If the replacement tank was the same size as the failed one it could still be too small- they should have done the math on the system volume and the difference in volume that occurs when the temp is raised by at least 80F, 100F would be better, to have some margin. The AWT on the system is probably something like 150F when the boiler out put is 160F, and the difference between a ~70F (when the system is cold) and a ~150F AWT is about 80F.

    The fact that you have big radiators rather than fin-tube, and from the photo it looks like at least some of the distribution plumbing is done in 2" or 2.5" piping, your volumes are going to be MUCH bigger than "typical" systems, and simple-minded sizing charts based on radiation type and boiler sizing just don't apply. It's conceivable that the installer just took a WAG at it or used a manufacturers chart and got it wrong. Monitor the pressure and temp as the boiler is heating up. If there is a clear temperature at which the pressure crosses 15psi. If that temp is under 150F it's an indication that the tank is undersized or not properly charged. If the system is set to 12psi when cold or tepid (long after the burner has last fired) ideally it wouldn't rise much above 15psi with a right-sized expansion tank, but NOTHTING LIKE 22psi (a 10psi rise). If it's been "normally" running at 25-26psi, it's anything but normal, if the cool or tepid pressure was set to 12psi. A 2-4 psi rise would be typical, and even a 5-6psi rise might be OK (but not ideal). With a 6psi+ rise at a high-limit of 160F, if you adjusted the high limit up to 200F (which is a perfectly legitimate thing to do) you'd be almost guaranteed to blow the PRV.

    Since you're getting a 10psi+ rise on the system you are likely hitting the designed acceptance limits of the expansion tank, beyond which the pressure then rise rapidly with temperature (which is when the PRV opens up to prevent a more destructive pressure release somewhere else on the system.) PRVs are not high-precision instruments, but those used on most hydronic systems are designed to open up at 30psi, which is the top operating pressure range of many hydronic system components, (including many cast iron boilers). There's usually a metal tag indicating it's design pressure, and I'm assuming yours reads "30psi"(?). If it's spittin' a coupla cups, it really IS hitting that pressure (or close to it), independently of what the 57 year old pressure gauge on the boiler says. If the PRV is also that old, it could be way out of calibration and opening up at lower pressures, but I'd still trust the PRV more than the pressure gauge. And if you're running 12psi tepid/15psi hot like it SHOULD, it doesn't really matter if it's kicking open at 25psi instead of 30psi.

    If you do your own system volume arithmetic you could play around with this sizing tool as a sanity check on the size of the tank that was installed. Or you can use the simplified instructions found here.

    In the meantime, note the temp at which the pressure takes off, and dial back the high-limit on the boiler's controls so that it stays below that temperature. If that temp is 150F you may be fine forever running the system at that temp, but if it's 140F it's a problem, since the return-water temp would likely be cool enough to cause destructive condensation in the flue and on the boiler's heat exchangers, and you may not have sufficient radiation to deliver enough heat at 5AM on the coldest day of the year at that temp. (If you DO have that much radiator, that's a very good sign for being able to hit mid-90s for system efficiency with a modulating condensing boiler under outdoor-reset control once the reset curves are adjusted.)

    The nameplate on the boiler probably has both input and output BTU numbers on it. If it's still readable, divide the output number by the input number- that's the absolute steady-state efficiency of the boiler when it was new. (Eg: if output=61,000 BTU/hour, and input =80,000BTU/hr the steady state efficiency is 61,000/80,000= 0.76, or 76% efficiency. A mid-50s boiler may be as high as 80%, but many were running in the mid-70s on day-1, by design. Standing pilot ignitions and lack of automatic flue dampers would typically bring the as-used average down to about 70% or less. Yours clearly doesn't have the damper, which would typically be mounted just above the dilution air hood (the black piece on your stack) where it enters the exhaust venting. It was a popular efficiency retrofit to add the automatic flue dampers in the late 1970s, and they became standard equipment new boilers to be able to pass minimum AFUE requirements that became code around that time.

    It's not worth adding efficiency enhancements to the boiler at this point- it's time to scrap it, say "good-bye" to your good-buddy and get something newer/better, and right-sized for your actual heat load. The heat load can can be estimated with reasonable accuracy from the name-plate efficiency of the old boiler and a mid-winter fuel bill with the meter reading dates, to measure fuel use against heating degree-day data. But a new boiler won't change the expansion tank requirements by much. (And it would be slightly smaller, not larger- the old boiler probably has something like 5 gallons in it, and a mod-con might have 1 or 2, but I'm guessing your system has several 10s of gallons in it. An oversized expansion tank works just fine.) If you replaced it with cast iron boiler you'd be limited to ~83% efficiency if you wanted to use the same flue, and even then it might require a reducing liner if the flue is too big for the right-sized cast iron boiler. Higher efficiency cast iron exists, but it's all forced-draft and would likely need more expensive venting materials than a mod-con, (narrowing the installed cost difference) and the very high end is ~87-88% AFUE.

  9. #9

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    Dana really appreciate the reply. Going to read through it a couple more times to fully grasp it. Something definitely not right because this morning the pressure was at 8psi at 100 degrees and now at 4pm the boiler is running at 23psi. Thats a 15 psi rise. I have the warranty service coming tomorrow to try to fix this but sometimes they don't know what they are doing so I like to have some idea of what I am doing to talk to them.
    I have posted on some other sites to try to get some help. One person suggested that they never should of put a bladder system on it and that most likely the expansion tank is too small. He recommended now that there is a new shutoff valve on the pipe going to the expansion tank that I should get the old steel expansion tank that is up in the ceiling hooked back up. And if I insist on staying with a bladder expansion tank that it should be a 60 instead of a 30, should be on the supply side before the circulation pump, and lastly needs some type of automatic air purger (said it is necessary when switching from bladderless to bladder)
    What do you think of this advice? Expansion tank on supply side vs return? Air purger for the system? Old steel bladderless vs keeping a new bladder expansion tank?

    Again I am really thankful for these answers. For strangers to take their time on forums and give knowledgeable advice is really amazing.

  10. #10

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    Also the following info might help
    Attached is a pic of the boiler info.
    There are 5 radiators on the 1st floor and 5 on the second. All are cast iron without fins. Listed are their dimensions. All are 20 inchs high including their feet. Length are 27,40,86,67,50,50,27,27,54,36 . Main pipe downstairs going to and from the system is 2 to 2.5 inches. The pipes leading up to each radiator is 3/4.
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  11. #11
    In the trades Dana's Avatar
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    With 135 in, 108 out this beastie was 80% efficient steady-state on day 1, might even hit 75% today. But with over 100KBTU/hr of output it's probably 3x or more oversized for the actual load if you have insulation in the walls & attic, and glass in the windows, which would mean with cycling & standby losses would put it in the high 60s, best case.

    Putting an air-scoop at the new expansion tank is always a good idea, and standard practice on new systems. The air scoop and expansion tank would still be part of the system if you slipped a condensing boiler or other replacement.

    And yes, the new expansion tank IS undersized- let them do the math on it since they're springing for the warranty replacement but if the tank was properly charged and the system set to 12psi there's no way you should be hitting north of 20psi if it were big enough (or bigger than needed). Don't be surprise if they put something that looks monstrously big by comparison in it's place.

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    Other than cost and the room it takes up, there is no such thing as a too big expansion tank. They can get monstrously heavy when they fail and fill with water, though, and need to be properly supported to account for that eventuality.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  13. #13

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    If given the option would you choose:
    1)reconnect to the old steel expansion tank in the ceiling? (only reason expansion tank was change was the isolation valve going to it wouldn't close. The plumber must of thought it was easier to just add an new valve and then add bladder expansion tank) Nothing is wrong with the old tank in the ceiling as far as I know
    or
    2)have them install a correct sized bladder expansion tank (60 or 90) when they figure it out. And also add an automatic air valve to the system (basically on top of a tee above the new expansion tank)

  14. #14

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    Just to give and update. Guy from warranty service came in. Explained the situation and he spoke to his supervisor. Said they were going to put a 60psi tank in. At first they said it would cost 165 to do it since they didn't not add the 30 in the first place. I tried to explain that by having someone else do it it actually made their job easier. They agreed to waive the charge.
    Supervisor said no air separator or Automatic air vent is necessary. That the radiators on the top floor are natural air collectors and just need to bleed them at the beginning of the season. Tried to tell them thats not what I read but I could see them getting piss off (whos this person telling us our job).
    I also asked them if they wanted me to drain the system to get an accurate count of gallons in the whole system. They told me there is no way they need more than a 60psi tank. I wanted to be certain that I didn't undershoot again?

    Any further thoughts guys
    Just to let you know. Last night at 2am temp reading was 95 and psi was at 7.5. This morning it hit 30 psi and discharged water. Temp was around 165. Thats a 23 psi jump.

    Just out of curiosity what is the supply side what is the return side. Is the supply side supplying water to the boiler or supplying water to the system/radiators. Same with the return side, is it returning water to the boiler or returning water to the radiators/system. Trying to understand if my circulator is on the return side or supply side. Same with the expansion tank - supply side or return side.

    thanks

  15. #15
    In the trades Dana's Avatar
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    Putting in a higher pressure tank is absolutely NOT a solution. A higher VOLUME tank is what's called for.

    The air scoop isn't an absolute necessity, but the system needs to be air-purged any time you break it open, regardless. (And bleeders at the top of the system are a tried & true method.)

    The max limits on many new cast iron residential boilers are 50psi, but most come set up with 30psi PRVs unless a higher pressure version is special-ordered. (Most residences aren't tall enough to require anything over 30psi.) Running/cycling them across wider pressure ranges than necessary (particularly a boiler that qualifies for an AARP card) risks stretching the bolt that hold the plates together, increasing the likelihood of leakage between the plates. Keeping it within a ~5psi pressure range from stone-cold-off to max system temp is how they were designed to be run, not cycling between 8psi-30psi at every firing.

    Your radiators are GREAT for low-temp condensing boilers, and are probably Burnham Sunrad or similar.



    The current versions look this:



    Open up a spreadsheet tool and start measuring.

    The Sunrad/Radiant and similar 20" x 5" radiators contain ~0.15 gallons per section and the sections are 2.25" long. So if you add up the total running inches and multiply (0.15/2.25=) 0.067 you'll be pretty close to the radiator volume. (eg: your 27" long radiator contains about 0.067 x 27= 1.8 gallons. Your 40" radiator contains 40 x 0.067= 2.7 gallons.)

    Any 3/4" copper plumbing runs about 1 gallon for every 40'.

    Any 2" iron plumbing (about 2.5" outside diameter) runs about 1 gallon for every 5.75'

    If it's 2.5" plumbing (about 3" outside diameter) it would run 1 gallon for every 4'.

    Figure the boiler itself has 5 gallons.

    Do your best guess as to the plumbing sizes and diameters that are buried in walls, chases, joist-bays, etc. but use a spreadsheet and add it all up, and you'll have at least a pretty good order of magnitude on the system volume you're dealing with. Then you can use the other standard arithmetic for sizing the expansion tank.

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