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Installed 5 new cast iron radiators replacing Slant Fins - now psi too high

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Jack_2
Jack_2 Member Posts: 38
I have a mixed cast iron, Slant Fin water heating system and just replaced 5 Slant Fins with new cast iron Governale radiators. Now, after running the boiler for only a half hour, the pressure rises to 45 -50 psi triggering the pressure relief to release water. My system is about 35 yrs old and is a 179k BTU unit with a large, old metal cylinder expansion tank that doesn't have an air valve and only a water release valve. Before I installed the radiators, max pressure was only about 20 to 30 psi and used to release water every few weeks from the expansion tank. Can any one here give me some ideas as to what might be the issue(s) here? Thanks.

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  • Gilmorrie
    Gilmorrie Member Posts: 185
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    Your conventional expansion tank must be water logged. Depressurize the system and vent and drain the tank - and refill. Don't install an automatic air bleeder with a conventional tank - it will deplete the air cushion. Good luck.
  • Jack_2
    Jack_2 Member Posts: 38
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    I already drained the tank multiple times with the same result. I don't have an air bleeder on that horizontal old tank and just have a water release valve on it. When you say depressurize the system, are you referring to releasing water from the pressure relief valve so the gauge reads 0 and then release water from the expansion tank? The pressure gauge on my boiler currently reads 10 - 15psi when cold. Thanks.
  • Jamie Hall
    Jamie Hall Member Posts: 23,543
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    There are two slightly different procedures, depending on whether you can isolate your compression tank from the rest of the system.

    If you can isolate the compression tank, do so. Otherwise, you will have to drain enough water from the system so that the pressure in the system is zero at the top of the boiler. Do NOT use the pressure relief valve for this. Use the boiler drain. If you are very careful indeed, you won't empty the pipes and the radiators; if you do you will need to purge and bleed in the usual way.

    Now with pressure off the compression tank, drain it right down to empty. Close the drain.

    Open the isolation valve to the tank or, if you had to drop the pressure on the whole system, raise the pressure back with the fill valve -- to about 15 psi, no more.

    Now I note that you say "I already drained the tank multiple times". If you drained the tank according to the above procedure and it filled right back up with water, it has an air leak. It will need to be replaced, and I would suggest a conventional expansion tank.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,746
    edited October 2021
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    @Jack-2

    Possibly when you added the CI radiators you increased the water volume in the system and now need a larger expansion tank.

    But the pressure rise your seeing seems a little too dramatic for that. Start over, drain the tank start with the system pressure at 12-15 then repressureize and see what happens.

    Your relief valve should open at 30...not 40-50

    Make sure all valves are open. Are you sure your auto feeder PRV is not leaking by? Tankless coil or indirect leaking city water into the boiler??
  • Jack_2
    Jack_2 Member Posts: 38
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    I didn't install the CI rads but had a plumber do this. He says I need a new expansion tank to resolve the problem but am hesitant since the system had normal pressure before the install. Obviously, the volume of water has increased due to the new rads, but wouldn't my old tank compensate for it? It's a pretty big tank that's ceiling mounted above the boiler. Since I'm new at this, the pressure on my system boiler is around 10 - 15psi and that's when I depressurize the tank meaning letting all the water out? How do I repressurize the tank if it doesn't have an air bleeder? Also, the relief valve is rated 45psi, is that too high for my system? I'd like to attach pics in JFIF format but don't know how to with url. Thanks.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,746
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    Most HW boilers the relief valves are 30 psi, It's possible yours is 45 psi, look on the tag on the relief valve.

    With a compression tank if you have a valve between the boiler and the tank you can close it and then drain the tank by opening the drain on the tank.

    When you are done and the tank is empty close the drain,open the valve between the tank and the boiler. You should here water refill the tank to about half way and te system pressure should be 12-15 psi.

    Start the boiler and when it gets up to temperature (180) or so your system pressure should be not over 24 psi max. If it is higher than that it sounds like an expansion tank issue.

    Adding more radiators with more water volume may require a larger expansion tank.

    Could it be something else, yes it's possible.

    A leaking prv adding water to the boiler, a broken vave that is shut but seems open + other things
  • Jamie Hall
    Jamie Hall Member Posts: 23,543
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    You don't have to "repressurize" the tank. Yes, you close the isolation valve and let all the water out of the tank, Then close the drain. When you open the isolation valve between the tank and the system, some water from the system will go into the tank and pressurize the air that's in there for you.

    If your system is set for 15 psi cold, you should wind up with about half air and half water in the tank. If you don't -- if the tank fills with water -- somewhere the air is getting out of the tank. Find it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jack_2
    Jack_2 Member Posts: 38
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    I do know how to drain the expansion tank but I don't hear water going in after the drain so maybe the valve is stuck shut even though I supposedly opened it. I also don't know how to drain water from the boiler without using the pressure relief valve. I'm attaching urls for the tank and the boiler in question. Thanks.




  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited October 2021
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    Jack_2 said:

    I have a mixed cast iron, Slant Fin water heating system and just replaced 5 Slant Fins with new cast iron Governale radiators. Now, after running the boiler for only a half hour, the pressure rises to 45 -50 psi triggering the pressure relief to release water. My system is about 35 yrs old and is a 179k BTU unit with a large, old metal cylinder expansion tank that doesn't have an air valve and only a water release valve. Before I installed the radiators, max pressure was only about 20 to 30 psi and used to release water every few weeks from the expansion tank. Can any one here give me some ideas as to what might be the issue(s) here? Thanks.

    I see three items of concern.

    1. When mixing cast iron and copper tube aluminum fin radiation on the same system you need to have seperate zones otherwise the heating will be uneven. Need more info on how your system piping is set up to determine if there is a problem or if the professional plumber resolved this.
    2. Most residential boilers have a maximum operating pressure rating of 30 PSI. There are some boilers rated at 50 PSI, but it is unlikely that you have one of those. The boiler rating plate will state maximum operating pressure. You should not operate a boiler rated for max 30 psi with a 45 psi relief valve. Someone may have added the higher pressure relief valve to fix a problem with a leaking 30 psi valve. If so, they were wrong to do that.
    3. The fact that a normal operation procedure of this boiler is to drain off water periodically "release water every few weeks" indicates that you have other problems.

    I suggest that you use the "Find A Contractor" option on this site to see if there is a qualified hydronics expert (Not just a plumber) to look closer at your setup. There is more going on here that just quick fix

    Respectfully submitted
    Mr. Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,746
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    It's possible that the gate/globe valve in the black pipe between the boiler and the expansion tank is stripped/broken internally and is not open or is only partially open
  • Gilmorrie
    Gilmorrie Member Posts: 185
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    When you drained the tank multiple times, did you vent the tank so that all the water was emptied and replaced with air? Or, at least did you drain the tank until the water went "glug, glug, glug" proving that air was being drawn into the tank. Post photos that show all the piping to and around the tank. Tell us exactly the procedure you uses to drain. You may have to break a pipe connection to really make sure the tank is completely drained and filled with air before refilling.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
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    Jack_2 said:

    I didn't install the CI rads but had a plumber do this. He says I need a new expansion tank to resolve the problem but am hesitant since the system had normal pressure before the install. Obviously, the volume of water has increased due to the new rads, but wouldn't my old tank compensate for it? It's a pretty big tank that's ceiling mounted above the boiler. Since I'm new at this, the pressure on my system boiler is around 10 - 15psi and that's when I depressurize the tank meaning letting all the water out? How do I repressurize the tank if it doesn't have an air bleeder? Also, the relief valve is rated 45psi, is that too high for my system? I'd like to attach pics in JFIF format but don't know how to with url. Thanks.

    Obviously more water in the system means that you need more room for expansion. What are the dimensions of the expansion tank? length x diameter? You my have a tank that is too small for the system to begin with. This caused the 30 PSI relief valve to release water regularly some 35 years ago. It might seem logical to just put a higher pressure relief valve on the boiler (if it were not a code violation) and just let the boiler operate at 30 PSI.

    If that same repairman were here today, I think he might fix your problem with a 75 PSI relief valve. DON'T DO THAT.

    Let's find out how much water is in your system then determine what size tank you need. You need a 5 gallon air cushion for every 100 gallons of water. In order to maintain a relatively small pressure change from cold start to the high limit operating temperature, you will need to multiply that 5 gallon cushion by a factor of 4 or 5 or more. So you may need 20 gallons of air space at 15 PSI in that tank. To get 20 gallons of air pressure at 15 PSI in the tank, you will need a 40 or 50 gallon tank to be filled with 20 to 30 gallons of water to pressurize the air in the expansion tank. Then you need to find a way to keep that air in the tank. This is all explained in @DanHolohan"s book Pumping Away. if you want to know the reason for your problem you should buy the book.

    If you just want the problem fixed then you need a hydronics expert that has already read the book. He is worth more than the plumber that does not understand the principles explained in the book and his prices will reflect that.

    Good luck with resolving your problem.

    Yours Truly,
    Mr. Ed


    PS what are the dimensions of your expansion tank

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Jack_2
    Jack_2 Member Posts: 38
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    Mr. Ed, I only changed the significant slant fins with CI rads as those rooms were bedrooms and bathrooms that had exposed exterior walls. The remaining slant fins are in hallways and internal rooms which are not bedrooms. My house is a 2 story brick semi detached 60'x20' that was built in 1948. I don't even think the slant fins are copper as it looks like standard metal pipes with fins. The dimensions of the expansion tank is 32" length while the circumference is 12". The specs of the boiler is a Weill-McClain model CGM-8-PI and is 192,000BTU with 50psi for water and 15psi for steam. Also, states min. relief valve cap at 192 lb/hr. I remembered the pressure relief valve that's rated at 45 psig on the label was replaced awhile ago.
  • Jack_2
    Jack_2 Member Posts: 38
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    Gilmorrie, to answer your question, I first shut off the water valve that's on the right in the first pic which leads directly to the tank then I open the valve from the tank and it drains maybe what looks like about a half gallon of water. Once it drains completely, I shut that valve and then open the valve on the right in first pic again.
  • Jamie Hall
    Jamie Hall Member Posts: 23,543
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    I'm going to assume that you mean the diameter of the tank is 12 inches. A 12 inch circumference is pretty small... and it doesn't look like that. If so, that's a 15 gallon tank. It may not be big enough.

    However, if you are only getting "about a half gallon" of water when you are attempting to drain it, either it simply isn't effectively connected to the system at all, or you simply aren't draining it. You should get about 7 gallons of water out of that tank when you drain it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jack_2
    Jack_2 Member Posts: 38
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    Jamie, you are right. I meant the diameter is 12". The hose attached to the tank goes directly to a drain, so I never could measure exactly how much water it is. Next time, I'll place the hose inside a big bucket to see how much really gets drained. My plumber now wants to install a 30 expansion tank. Do you think that's sufficient for my system based on my previous specs and new rads? Thanks.
  • mattmia2
    mattmia2 Member Posts: 9,840
    edited October 2021
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    Is the cap closed on the automatic air vent on the boiler? It should be so that it can't vent air. If that vent is doing its job it would remove the charge from the tank over time. There should not be automatic vents in a system with a conventional compression tank like yours.

    In fact it probably should be piped back in to the tank with an air fitting.
  • hot_rod
    hot_rod Member Posts: 22,353
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    Or just install a #60 Extrol tank.
    A diaphragm tank will be about 2/3 the size of a compression tank
    also add a good air purger. Personally I’d add a DiscalDirtMag to handle air, dirt, and magnetite
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Steamhead
    Steamhead Member Posts: 16,942
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    Jack_2 said:

    Gilmorrie, to answer your question, I first shut off the water valve that's on the right in the first pic which leads directly to the tank then I open the valve from the tank and it drains maybe what looks like about a half gallon of water. Once it drains completely, I shut that valve and then open the valve on the right in first pic again.

    There's your problem. You're not draining the tank completely.

    What you need to do is close the valve in the tank line. Position a bucket under the drain and open the drain. Some water will leave the tank, then you'll hear air being sucked in with accompanying "glug" sounds. Let this process continue until you no longer hear air being sucked in, which may take up to an hour. Then close the drain, open the tank line valve and you should be good to go.

    I like to install special tank-draining fittings on the systems we service, which are designed to let air re-enter the tank as it's being drained, speeding up the process. But that tank would need some piping changes to make this work. To me it would be worth it- I prefer this type of tank since it has no moving parts.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
  • Jack_2
    Jack_2 Member Posts: 38
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    Ok, I finally fixed the problem all thanks to you guys! Apparently, as Steamhead pointed out, I was not draining the expansion tank properly and my air purge valve on the boiler was completely open. Initially, when I started draining the tank, a flush of water came out for about 2 minutes and then a trickle of water. I thought that was it but that trickle of water needs to drain for about an hour and a half until it was completely empty and the pressure gauge pointed to zero. Also, as mattmia2 stated, my air purge valve was open and it needs to be closed for my setup compression tank. Once that was done, I turned my boiler on and the pressure rose to a steady 17psi with continuous running. Even though that pressure seems to be low, all my rads became hot even on the second floor. I was just wondering why my plumber used copper tubing as opposed to Pex piping for the new rads. Wouldn't it have been easier for him to work with flexible tubing so the rads can be moved if need be? Just want to say again you guys saved me a lot of headaches not to mention money as well. Time for me to look for a real pro than a wanna be ripoff plumber.
  • Jack_2
    Jack_2 Member Posts: 38
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    Forgot to mention that the reason I have a rated 45psi pressure relief valve is because the boiler I have is a Weill-McClain 50psi 197,000BTU unit. I guess the previous guy who installed it looked at the specs of my specific boiler.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,746
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    @Jack_2

    Most on here would consider copper superior to pex.

    Why don't you post the model of your boiler so we can see what the pressure rating would be?
  • Jack_2
    Jack_2 Member Posts: 38
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    EBEBRATTT-Ed, I already did. Please see my post on 10/27 above. I'll post it here again. The specs of my boiler is a Weill-McClain model CGM-8-PI and is 192,000BTU with 50psi for water and 15psi for steam. Also, states min. relief valve cap at 192 lb/hr. I remembered the pressure relief valve that's rated at 45 psig on the label was replaced awhile ago.

    Ed, since this boiler must be at least 35 yrs old, what super efficient boiler would you recommend replacing this one? Thanks.