indirect hot water heater coil leaking...

Discussion in 'HVAC Heating & Cooling' started by pete c, Dec 14, 2007.

  1. pete c

    pete c Member

    Dec 14, 2007
    ... again.

    6+ years ago I moved into my current house. I installed a new AO Smith 4 section boiler and a Bock 50 gallon indirect. After about 4 years, give or a take a few months, I get a call from the wife at work.

    Wife-"THE BASEMENTS FLOODING!!!!!!!!" She says in a rather panicked voice.

    Me-Where's it coming from?

    wife-The side of the "furnace"!!!!!

    me-Crap. Go down there and close the valve going into the boiler. It is above and to the left of it.

    wife-"What the #$@! is a boiler!!!!!"

    me-The furnace.

    wife-Oh. Wait a minute. I turned it off. Water is still coming out

    me-did it even slow down?

    wife-no, I don't think so.

    me-f##K. go back down and shut off every valve you can reach.

    wife-OK.....did it. it stopped.

    I got home that night, went down into the basement, scratched my head for a minute, turned the boiler feed back on and waited.



    Then I turned the domestic feed to the indirect back on. Guess it fixed itself, I thought/hoped......for a few seconds till the boiler pressure relief valve popped again.

    I shut the domestic feed off again and after a few seconds the water gushing out of the "furnace" stopped.

    WTF, I thought to myself? After thinking about it and experimenting a bit, I came to the conclusion that my domestic supply was pressurizing my boiler. Apparently there was a leak in the boiler water coil.

    I went and dug out my bock manual and warranty info. I read back through it, a bit more carefully tha when I installed it. I found the part about checking the anode.

    Anode? What's an anode?

    Now I knew what an anode was.

    After being bounced around a few different places, I got a hold of a bock rep and they replaced it, which kind of surprised me as I figured they'd say DIY install? pffttt. sorry.

    Anyway, a few weeks later, I had my new bock. I got by just fine on my tankless coil till then.

    I have performed the anode check since then. I have replaced it once and was getting ready to look at it again when I hear another panicked call from the basement.

    daughter-Dad? There's water comingout of the furnace.

    me- crap.

    So I went back down, shut off the domestic HW supply and watched as the boiler pressure eased it's way back down.

    Looks like I got another cracked coil. Bleep me.

    I emailed the bock rep again and am waiting to hear back from him.

    I am considering just living with the tankless coil. I only have one problem with the coil and that is that you do get a fluctuation in temp, but, it ain't that bad.

    Also, I have another idea for the Bock.

    I plan on installing radiant heating sometime in the next year or twenty. I also like to burn wood in my stove. I was thinking running some black pipe around inside the woodstove and circulating water from the bock, thereby using the woodstove to keep the bock hot. I would then use this water to heat the radiant system.

    I would also circulate water from the boiler to the bock to keep it hot when I am not running the stove.

    Not sure if I have the room inside my stove to do this, but, I might be able to go to a larger stove.

    Am I crazy or what?

    One other question.

    I was thinking about just keeping the existing bock heater but plumbing it differently.

    Tell me if you think this is feasible.

    I run my domestic supply through the tankless coil to the indirect domestic supply. On the hot indirect out I install a T back over to the supply going to the tankless coil. I put my existing recirc pump in this. I would cap off the boiler feed and return water going to my leaky coil.

    So, now I have my indirect being supplied with hot water from the tankless coil. When the indirect temp drops below a set temp, it's water gets recirculated back through the tankless coil.

    This should give me the nice even temps I have come to expect from the Indirect, without having to get a new one.


    Last edited: Dec 14, 2007
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    If the T&P valve from the boiler is leaking, check and probably replace the expansion tank. The T&P valve could be bad as well.

    You have an expansion tank on the WH also, or probably do, and if that was bad, the WH relief valve would open.
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  4. pete c

    pete c Member

    Dec 14, 2007

    wish that was the problem. it would be a cheaper fix. but, I'm afraid it's not. the amount of water coming out of the valve is too great and the problem goes away when the indirect tank is isolated from the boiler/hydronic heat system.
  5. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    I'm not sure I understand the configuration but let me describe what I think it is. Where I am wrong you can correct me and we can go from there.

    You have a boiler with a tankless coil that is immersed in the water side of the boiler.

    Your indirect heater was heated by circulating water directly from the water side of the boiler (not from the tankless coil) through a coil in your indirect heater.

    The coil in the indirect heater failed and pressurized the water side of your boiler.

    Now you have connected the tankless coil, which is supplied with your water source, directly to the indirect heater. The indirect heater supplies your hot water faucets.

    Possible fixes:
    1. Continue using what you have; or
    2. Replace the indirect heater with an electric water heater that will be suppllied via the tankless coil.

    I never had an indirect heater but had a tankless coil. It had a hard time keeping up in the winter when we are supplied with 33F water so I run it through an electric water heater. The electric heater rarely turns on but it buffers the flow so I get steady water temperature. The electric elements would top it off if necessary but the temperature is set well below the boiler operating temperature.

    I was using a lot of oil in the summer just to keep the boiler hot. Now I just turn off the boiler in the summer and let the electric supply the hot water. Even though the electric BTUs cost more the net cost is less because there is less warm air going up the stack while the boiler is kept hot.
  6. pete c

    pete c Member

    Dec 14, 2007
    that's pretty close, bob.

    I have the indirect still connected normally to the boiler. I also have the domestic supply for the indirect going to the boiler tankless coil. The return from the tankless coil goes to the output of the indirect. Basically the tankless coil and the indirect are plumbed parallel to one another. I have a ball valve in the supply to the tankless coil and one in the supply to the indirect. There are also ball valves coming and going to the boiler water lines between the indirect and the boiler.

    Currently I have the ball valves between the boiler and indirect closed and the domestic feed to the indirect closed. This keeps the indirect from pressurizing my boiler water and also keeps the now cold indirect water from flowing when I turn on domestic hot water.

    Essentially, right now I am just operating off the tankless coil.

    I gave some thought to your idea about using the tankless coil to feed an electric heater. So long as the electric heater is well insulated, it should rarely have to rely on electrons to heat it. It also smooths out the temp fluctuations. As for the wisdom of shutting down the boiler side to run off electricity during the summer, I don't know. I have talked to plumbers who say shutting down your boiler for extended periods does more harm than good. Also, if you use quite a bit of hot water, I think you might still save money using oil to heat it rather than electricity. I use oil year around and it seems like I burn damn near nothing, till I turn on the heat.

    Well, if you weren't confused before, you should be now!

    Wish I could draw pictures on this board.
  7. CHH

    CHH New Member

    May 25, 2007
    Denver, CO
    Pete - a couple comments:

    I think you've described things fairly well. Your comment about drawing pictures is a common desire. You can post pictures (or drawings saved as pictures) in this forum using the "Attach Files" option.

    Your concept of continuing to use the indirect as a storage tank but recirculating for heat when it cools would work. The way I see it you'd have to use a bronze circulator since it's a pot water system. Maybe it should have a backflow preventer upstream of the coil and recirc tee. It should have a check in line with the circulator so the coil and storage tank aren't inadvertantly by-passed.

    Have you thought about using a different brand of indirect? HTP uses metallurgy rather than coatings to resist corrosion and they have a lifetime warranty.

    The comment on shutting down a boiler might need some examination. If the heat exchanger in the boiler is a welded unit then seasonal shut down is not an issue. If the heat exchanger is built-up with seals between segments then cooling it down can cause leaks.
  8. pete c

    pete c Member

    Dec 14, 2007

    Thanks for the suggestions. I had thought about adding a check valve, but, I was thinking that the recirc pump served as one. If not, then I would obviously need one. I think my current indirect recirc pump may be brass. I'll have to check.

    There is one concern I have. If the recirc pump comes on while hot water is being used, would it reduce flow much? I doubt it, but, it is a thought.

    As for my boiler, it is a regular cast iron 4 section one. So it does have gaskets and I don't suppose they care to be heated/cooled very much.
    Last edited: Dec 15, 2007
  9. pete c

    pete c Member

    Dec 14, 2007
    Well, after a few months of living with the tankless coil, it is time to do something. I get all the hot water I need from it, but, the temp fluctuations are a real pain in the ass.

    So, I have two options, installing a brass circulator pump to use water recirculated through the tankless coil to keep the indirect tank up to temp or as was suggested earlier in this thread, buying an electric HW tank and supplying it through the tankless.

    The first option is cheaper (I think) and involves a bit more plumbing, but not much. The second option gives me the ability to shut down the boiler and still have hot water. But, from what I gather, letting a cast iron 4 section boiler get cold may lead to leaks.

    Any further suggestions would be appreciated.
  10. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    You could also use the indirect heater as it is supposed to be used, by supplying the heating coil of the indirect heater as a zone of your heating system. You would not need a new pump if your current circulator has enough capacity.

    You could also, at the same time, run the output of your tankless coil to the DOMESTIC SUPPLY connection of the indirect heater.

    The result is that the storage in the indirect heater will moderate the temperature variation from the tankless coil, and the circulation from the boiler will make up for any inadequate capacity of the tankless coil during high demand.

    A decision to install an electric unit could be based on usage of fuel in the non-heating season. Look at your records of fuel usage during the non-heating season and see if you would save by using electricity to heat water in the summer.

    I would not try to heat domestic water with a wood stove unless that stove had a complete control system and safety system designed for that purpose. It is not a simple job to control the temperaure of a wood stove and the usual temperatures in a wood stove will develop enough steam pressure to blow up any domestic system.
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