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Thread: Have some issues with hot water boiler system

  1. #16

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    Dana sorry to have wasted your time with last post. Did not reread it. I didn't mean 60psi expansion tank. I mean jumping from a size 30 to a size 60. Radiators look just like the top picture you have. I'm just going to measure volume today and be done with it. I have a 5 gallon bucket and the sink is right there. I'm going to shut off the boiler. Turn off the gas and start draining. when I get lower i'll open the radiator bleed valves. Anything else I should know about draining and refilling a system?

  2. #17
    In the trades Dana's Avatar
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    Draining the complete system just to swap expansion tanks is a bad idea if you don't have to. Once you've add that much air to the system you could spend quite a bit of time and energy purging enough air just to get flow into the radiators(!), and even then you'd have bubbles to purge that could vapor-lock it a few hours or days after the initial purge. (That's why automatic air scoops are handy- even if there's a bit of gurgle on the system it'll usually burp the rest eventually as long as there is flow.)

    Air in the system is hard on pumps, and the fresh water has oxygen in it to corrode stuff, whereas the "dead" system water has very little. Save as much of the system water as you can, and purge air only as-necessary.

  3. #18

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    Jumped the gun Dana. I drained the system to find out exactly how many gallons it held. Hopefully it wasn't too bad for the system. I started draining it at 12psi. 47.5 gallons came out. The first 2.5 gallons brought it down to 0psi. So I'm not sure if its considered 45 gallons or 47.5.
    There are 2 temperature gauges. Inside the boiler - which never goes below 95 and i've seen as high as 170. Then there is a thermometer on a return pipe. I've never really paid attention to that temp. The room is usually between 60 and 70 degreees.

    Is the 30 enough and do i have some other problem or should a 60 be on it?

    thanks

  4. #19
    Retired Defense Industry Engineer jadnashua's Avatar
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    http://www.watts.com/pages/support/sizing_ET.asp is a handy calculator to determine the volume required. Knowing the volume and temperature swing and system pressure, it will give you the info you need to pick a tank of sufficient size. Each company has their own model numbers that correspond to a certain size...they are not likely generic, so 30 or 60 are meaningless unless attributed to a specific brand.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #20

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    according to watts I have a calcualted acceptance value of 1.15 and calculated total volume of 3.17 (and thats making it 50 gallons and the temp change slightly greater). According to the tank I have on it now it (proflex2 30) its capacity is 4.8 and accepted volume is 1.9.
    I should be fine with this one. I guess something else is wrong and I probably don't need the bigger tank?
    Funny thing is now I can't get my pilot light back on in the boiler. Feel like i can't win. Going to have to search the forums for that

  6. #21
    In the trades Dana's Avatar
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    The numbers you got out of Watts selector is only if you want to let it run all the way up to the 30psi limit, which you don't really want to do.

    You have more than 50 gallons of water total in the system, even if you were draining it from the very bottom of the boiler. The boiler has something like 5 gallons or more in it all by itself.

    Using the Watts tool, set volume to 55 gal, both the pre-charge & autofill to 12psi, and pressure relief number to 20psi (the very high end of the pressure you'd ACTUALLY want to see if you're starting at 12psi when the system is stone-cold). Using 100F/200F for temperature range and the tool gives you a minimum expansion tank volume volume of 8.8/1.6 for volume/acceptance. If you dial the temperature range back 100F/180F it gives you 6.6/1.2, which gets you within 7.2/2.9 limits of the Flex2Pro HTX60.

    The HTX30 is only good for 4.8/1.6 which is marginal at best. If the system was 12psi at a cold start of 65F and the high-limit set to 170F, the minimum sizes calculated by the Watts tool is 3.88/1.4 for a 30psi relief valve. Bumping just the temp to just 180F brings it to the hard limit on acceptance volume for the -HTX30. If the system actually has more water than 55gallons you're toast (as the symptoms seem to suggest!).

    The HTX60 should keep it from spitting water in your operating range unless the true system volume exceeds 55 gallons by more than just a little bit.

    Purging air from a fully drained multi-story system can be a bit of a pain. Note that you'll be starting with COLD 50-55F water- you may have to bleed more water out of some as the thing comes up to the operating temperature range to keep it down to ~12psi @ 100F boiler temp. Hopefully you'll find a bleeder valve (or valves) at the top floor of the system- open it up during the initial fill and fill until it stop gurgling & spitting air. You will likely need to run several 10s of gallons out of the bleeder before enough air is purged to get it to that point, and you're guaranteed to still have air elsewhere in the system, so this may be an iterative process. It may flow fine for awhile, then develop a bubble at the top of the system interfering with flow, which you can then bleed off with the bleeder valve until it's running clear with no fizz, readjust the pressure, repeat as-needed. (Be really careful if bleeding it while the system is hot.) Bleeder valves are often (but not always) located at a radiator, and many/most systems will have an automatic air trap/vent to aid in purging the last bits of air as the bubbles work their way to the top of the system while it's running once you have it purged well enough to get reliable flow.

    The temperature gauge on the return water line is important for monitoring the operation of the system. It's OK if it's running cooler on start up, but if it spends most or all of it's burn time with return water below 130F it can damage the boiler with condensation on the heat exchanger plates or damage a masonry/terra-cotta flue with flue condensation. Natural gas exhaust condensation is mildly acidic, causing corrosion on iron boilers an breaking down the mortar holding the masonry together if it's chronically condensing. Most systems are set up with a 20-25F delta-T, so if the boiler's output is normally 160-170F, the return water temps will be reliably above 130F, except during start ups (which is fine.) If you swap in a condensing boiler you would then want to lower the temperatures as much as possible to reap the highest efficiency, which is why they use acid-resistant plastic exhaust venting rather than venting into masonry chimneys.

  7. #22

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    Dana great info- thanks.

    I played around with the Watts calculator. Temperature doesn't change it that much, even if I use room temp as the lowest setting not aquastat temp. But moving that pressure release valve number from 30 (which is what I entered) down to 20 really makes it bigger. Also the drain is all the way on the bottom of the boiler (included pic). Not sure how much more water was left in the actual system. Good news is there is now a Amtrol Extrol Model 60 on there along with an Auto Air vent on the branch of piping going to the expansion tank.
    The figures for the Extrol Model 60 are 7.6/2.5. Also from this site ( http://www.pexuniverse.com/docs/pdf/...tank-specs.pdf ) they tell you what model Extrol should be used depending on BTUs and based on Max temp. I've including a screen shot of those charts below. My system matches up well with the model I have now.

    I'm going to reread the second part of your reply to fully comprehend it since you are spot on with a lot of it

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  8. #23
    In the Trades Tom Sawyer's Avatar
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    Awful lot of conversation and figgerin here when anyone that works with this stuff could have told you that your expansion tank was too small. What you have there looks like an old steam to forced hot water conversion or a monoflow system, both of which have large piping and radiators and lots of water.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  9. #24
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    You have a leak. Adding fresh water to a closed loop hydronic heating system is never a good thing.

    12 psi is common and sufficient and typically will not change regardless of pump or operating status (that is what the expansion tank if for). The system or boiler pressure relief valve should never go of, weep or leak. The expansion tank is correct. A new condensing boiler is the right and only choice. Be sure that you have a Manual 'J' heat load analysis performed before buying any boiler from any body.

    Merry Christmas to all.

  10. #25

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    Tom Sawyer - It is a venturi monoflow system. I'm pretty sure it was always hot water.

    BadgerBoiler - New boiler or not I'd still have to fix the leak if there was one in the system right?

    With the new expansion tank there has not been a discharge of water for 2 days . However the pressure has consistently been at 22-23psi while running. Is there any chance I need a bigger expansion tank to get the psi down while running?

  11. #26
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Many older boilers develop slow leaks between sections and over the burners. Weeping between cycles water lost is evaporated and never seen. Just a thought. Oh, and many pressure gauges lie.

    Lower the pressure until the highest vent sucks air and add 3-5 psi...call me in the morning.

  12. #27
    Retired Defense Industry Engineer jadnashua's Avatar
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    You need water pressure in the boiler for two reasons: to keep the water from flashing to steam when passing by the heat exchanger and to keep things from boiling and enough to keep things from boiling when passing through the pump and creating cavitation there. Cavitation is both noisy and can damage parts. Excessive pressure puts a lot of stress on things - they work best when the pressure is stable. The expansion tank normally keeps the pressure within a pound or two unless there's a problem elsewhere.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  13. #28

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    Jim - I'm getting some advice on some other forums that a 10psi increase is perfectly acceptable in a system with 50 gallons in it. And that systems that only change a couple psi are the new 10-12 gallon systems. I'm a little confused at this point.

    BagerBoiler- I understand that you say the boiler itself might be leaking. Not really following what you mean when you say "Lower the pressure until the highest vent sucks air and add 3-5 psi" . With the fill valve shut off, if the pressure never goes below 12psi I should be okay right? Right now I am still getting some air in the top radiators from draining the system. Once all air from the system has been removed if the pressure doesn't drop below 12psi when cold I am good right?

  14. #29
    Retired Defense Industry Engineer jadnashua's Avatar
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    If the expansion tank is sized properly, the pressure shouldn't rise much between hot and cold. Older boilers don't like big pressure swings (well, most of them don't, new or old) - it can literally stretch the bolts holding the heat exchanger when hot, and when it cools, those bolts may not spring back, thus leaving less tension on the sections of the heat exchanger. This can allow it to leak. But, since it is a part that gets hot, that liquid usually just evaporates or is boiled off the outside, and doesn't show up as a leak unless you look very carefully.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #30
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    I believe they are referring to a #60 (60#) diaphragm expansion tank. I doubt very much that it is required but would start by lowering the max operating temperature to confirm. The existing expansion tank is bad or you have a valve over-filling. These are the only two choices. If the 30# pressure relief valve goes off the resulting pressure should remain the same through a 24 hours cycle.

    No scoop is necessary in the typical cast iron radiated system.

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