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Replacing Boiler Expansion Tank

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by Dana B, May 23, 2013.

  1. Dana B

    Dana B Feeling the Heat

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    I am in the process of of having a pellet boiler installed but will be leaving my existing oil boiler in place.

    The oil boiler is leaking water though.

    I have water leaking from the pressure relief valve at a pretty steady pace. It fills up a large mop bucket in about 2-3 days time.

    The expansion tank on the oil boiler was mounted sideways rather than vertically. It is unsupported and is sagging. However when the near side of the tank (what would be top if mounted vertically) is hot while the far side (what would be bottom if mounted vertically) is cool and it does sound like there is air in the tank when performing the knock test. This seems to indicate a working expansion tank. Does this mean that the expansion tank is not likely the cause of the PRV leaking?

    Another symptom is that the system always seems to have zero pressure according to the boiler pressure guage. I believe the pressure guage is working because if I hold the pressure valve open I can see the pressure increasing on the guage.

    Any ideas on what might be causing the leaking and zero pressure?

    Thanks guys

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  2. maple1

    maple1 Minister of Fire

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    I'd suspect both a water logged tank and a bad pressure guage. I've had both happen. If it's non-bladder tank, they are commonly mounted horizontally - and also susceptible to water logging. If it's a bladder tank and gotten to sagging, that could also be a sign that maybe the bladder has a leak in it & it's filled with water. I'd plan on replacing both - a pic of the tank might help. Also a sagging tank has got to be stressing something else that I'm sure you wouldn't want to break. While at it I'd also try to find a way to get two pressure guages on your boiler/system. Redundancy is a good thing when it comes to those. Make sure the new tank is pressurized the proper amount when you install it.
  3. stee6043

    stee6043 Minister of Fire

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    Well a leaking pressure release valve certainly could be the cause of pressure loss. If you fill and increase pressure does it hold for a while or immediately go to zero?

    For what it's worth my experience has been that pressure relief valves are almost a normal wear item. They go bad and are easily replaced. Most folks around me have replaced one or more on their domestic hot water heaters. It's a 10 minute job.

    What PSI is your pressure relief valve? Certain sizes/ratings are readily available at your local Home Depot, Lowes or Menards. If you have an oddball size you may have to get it online (perhaps Amazon). Isolate the leaking valve, pop it off, replace with new, see how she works. Should be a $20 fix??
  4. maple1

    maple1 Minister of Fire

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    Is it possible for a PRV to leak if there is zero pressure in the system? With a guage reading zero, and the PRV leaking as much as it sounds, I'd still bet on the guage being bad as part of the issue. Of course, all of these are now suspect items - but all fairly easy to remedy. I would also perhaps question the cold water feed regulator - it should limit the system pressure build-up from incoming fresh water. I keep my fresh feed valved off and only open it to replenish if my pressure gets low. The PRV should have a little flippy handle thing on the side to bleed water out of - did you try letting a bunch out through that? Could also be a piece of dirt in there that might get flushed out doing that. Shut your feed off before doing that though.

    Right now I'd be worrying about what that sagging tank is stressing...
  5. Bob Rohr

    Bob Rohr Minister of Fire

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    How old are these components? 15 years or more? Do a complete trim replacement.

    I'd replace the expansion tank, mount a bladder or diaphram tank upright if possible, the relief valve, probalby a 30 psi valve on a residential boiler, and a new autofill valve.

    You can buy boiler trim kits from most hydronic brands, Watts, Amtrol, Caleffi, Honeywell it would give you all the components you need at a package price.

    If the gauge needle moves, it is probably ok. The older gauges were of much better quality, compared to what you find today.

    Then confirm that the system is leak free, fill and pressurize, mark the gauge reading and let it set a few hours without operating to see if it maintains pressure.
    BoilerMan likes this.
  6. maple1

    maple1 Minister of Fire

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    When my guage went bad, it read a number & the needle still moved (it was about 15 years old). But it just read about half of what the pressure was. I'd do everything Bob mentioned, plus add on two new pressure guages - or maybe a pressure guage & a tridicator.
  7. Dana B

    Dana B Feeling the Heat

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    boiler pic 1.JPG

    Thanks for all the advice guys.

    I have included a picture of my system showing the expansion tank above.

    If I increase the pressure on the boiler it seems to stay at pressure according to the pressure guage. At least for a few minutes while I am in the basement looking at it anyway. But it always go back to zero. I just haven't monitored closely to see how quickly it goes back to zero.

    I have not had a chance to check the pressure rating on the PRV yet.

    The house was built in 1999 and it is the original boiler. I am assuming that most if not all of the parts on the boiler are original.

    I think I will replace both the bladder expansion tank and the PRV. The expansion tank that's on there now is an Amtrol 30 12psi from factory and 100 psi max. I've heard that a couple of psi should be added to new ones out of the box before putting them in. What do you guys think about that? I had planned on replacing it with the exact same model but I can't easily install it vertically and quite frankly I don't want to do it if I can get away with installing the new one sideways and supporting from the cieling.

    What is the autofill valve and where is that usually located?

    Also no one mentioned the air separator. It's a taco and it looks like there is a valve that sits in it that is leaking a minute amount of water. How does this figure into the equation?

    I'm not in the plumbing/heating industry as many of you but rather I'm a DIY homeowner trying to educate myself to save money and the advice you have to share is invaluable and I am very grateful for it.
  8. maple1

    maple1 Minister of Fire

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    DIY here also.

    The autofill is the bronze color thing with the lever on top, front & center in the pic right above the aquastat. Those can also get some dirt in them & stay open a bit all the time, which puts way too much pressure on your heating system. I keep mine valved off. The lever is for fast filling, if you lift it up it will let water run in with no pressure regulation.

    You can pretty well mount the expansion tank anywhere that is convenient, and just run a pipe to it from where it's screwed onto now. Can you strap it to your joists up above? The way it looks there it looks like it got too heavy on one end (water inside), therefore bent - but I don't think they're designed to be mounted like that. When replacing the tank I would also put a T in between it & the boiler & put another pressure guage in it - very cheap & easy to do while you're doing the tank. I would also put a valve in there too so you can temporarily isolate the tank (not sure thats kosher but its what I would do). Not sure about your system (one storey? two?), but mine (2 storey) works great with 10psi. I wouldn't run a whole lot more than that. So say for 10, on putting in the new tank, you would check that there is 10 psi of air in the tank (& no water), and 10 psi of water in the boiler/system, then you would open the connection between the two. Do that when the boiler is on the cold side of its operation cycle. Leaking from the air separator might also indicate higher pressure than there should be - could also just be a leaky bleed fitting too.
  9. Dana B

    Dana B Feeling the Heat

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    I am going to take Bob's advice and replace the expansion tank, pressure relief valve and auto fill valve. I picked up the parts today on my lunch break and will be doing the work this weekend.

    Prior to doing it I had planned on shutting off the boiler to let it cool down, shutting the main water feed valve, and relieving the pressure. Is the best way to relieve the pressure via the PRV and when I turn it back on do I use the autofill valve to bring it back up to pressure?

    Any other safety precautions that need to be taken or steps that I missed?
  10. Dana B

    Dana B Feeling the Heat

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    I did the work over the weekend and everything went well. After replacing the PRV and the expansion tank I had planned on replacing the autofill valve as well but the problem seemd to have been fixed already. No leaking and constant pressure around 15-18 psi now. it was much easier than I thought it was going to be.
  11. maple1

    maple1 Minister of Fire

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    Sounds good. Was there any water in the air side of the tank?

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