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Correct Way to Abandon Tankless Coil

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MichaelG
MichaelG Member Posts: 26
For fuel economy reasons, I'm discontinuing use of the tankless coil in my 2004 Burnham V7 oil-fired HW boiler.

In its place will be a Rheem 50Gal Hybrid HWH. I'm pretty excited to have a water heater with wifi...

Question- The tankless coil in the boiler will remain in place, but what is the safest/best way to do so? Ideas:
1- Simply shut off the valve on the cold water inlet side
2- Cut and leave open the inlet/outlet piping
3- Cut and cap the inlet/outlet piping

It seems that Option 1 leaves me with a redundant DHW source if I happen to need one in the future (unlikely)

Option 2 seems to mitigate the risk of pressure buildup inside the coil that might occur if capped. But it also means if the coil springs a leak in the future (does this ever happen?) then I could end up with water shooting out of the open pipes

Option 3 seems the least risky overall, provided that there's not an issue with the pressure created by the capped coil.

If I go with option 3, should I make an attempt to siphon/blow the remaining water out of the coil before capping it?

Thanks everybody.

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    Option 2. It is very unlikely to spring a catastrophic leak all at once, so assuming you look at the boiler from time to time you'd notice it before it became a problem. I've never been fond of option 3, although if I were to do it I'd cap one end and put a pressure relief valve on the other, rather than a cap.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,633
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    Option 1 will keep it as a back up

    But

    It's not just the piping. You have a low limit control that will maintain the boiler water hot all the time. This will increase energy use. You have several choices.

    1.. Just shut the boiler switch off in the summer. It still will maintain hot water in the winter.

    2. disable the low limit. This may not be able to be done with some controls.
    3. Or leave it as is. Many recommend keeping the boiler hot. If so set the LL at 130 deg.
  • Leonard
    Leonard Member Posts: 903
    edited April 2018
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    Could do option 2 , but I'ld do preservation to keep bugs from crawling in and plugging the tube. Basically "cap" off the pipe with about 8 layers of aluminum foil folded over ends and "tightly" wired on.
  • Fred
    Fred Member Posts: 8,542
    edited April 2018
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    If it were me, I'd just remove the coil and put a couple plugs in the boiler block/block plate. The likelihood of you ever using it as a backup is almost zero. Easier to buy and install a new water heater than fuss with reconnecting this coil and then disconnecting it again plus install a new water heater.
  • newagedawn
    newagedawn Member Posts: 586
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    the easiest way i know is to leave it in the boiler and cut the cold water feed and the hot out pipes and leave them open to the atmosphere
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • frankjc
    frankjc Member Posts: 38
    edited September 2020
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    Option 2. It is very unlikely to spring a catastrophic leak all at once, so assuming you look at the boiler from time to time you'd notice it before it became a problem. I've never been fond of option 3, although if I were to do it I'd cap one end and put a pressure relief valve on the other, rather than a cap.

    I am about to do this in my house. What sort of pressure relief valve would work. There is a Watts 100XL attatched to it right now. Would that relieve pressure (i am assuming air) that whould build up in an empty coil?
    My other thought was to simply unscrew the valve and leave a bucket under it, in case it ever springs a leak.
  • pecmsg
    pecmsg Member Posts: 4,894
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    Replace the coil plate with a blank plate or just cut the lines and leave open. They won’t just Fail they’ll begin leaking slowly and get worse
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    frankjc said:


    Option 2. It is very unlikely to spring a catastrophic leak all at once, so assuming you look at the boiler from time to time you'd notice it before it became a problem. I've never been fond of option 3, although if I were to do it I'd cap one end and put a pressure relief valve on the other, rather than a cap.

    I am about to do this in my house. What sort of pressure relief valve would work. There is a Watts 100XL attatched to it right now. Would that relieve pressure (i am assuming air) that whould build up in an empty coil?
    My other thought was to simply unscrew the valve and leave a bucket under it, in case it ever springs a leak.
    The problem isn't air. The problem is a two step failure -- admittedly rare, but it has happened. The first step is a leak -- it can be a pinhole -- which allows water to get into the coil. The second step is that the boiler overheats, and that water boil, or tries to. The resulting pressure can be quite enough to blow the caps off the coil, or split the pipe, with results ranging from relatively minor to quite catastrophic.

    If you object to having an open end, which is goof proof, at least put a pressure relief valve rated at no more than the boiler pressure (often 30 psi).
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • frankjc
    frankjc Member Posts: 38
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    I am on the fence about just having it open. What kind of relief valve would I use? Would it connect where the existing valve with the yellow tag is?
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    A standard hot water boiler relief valve, rated at the same pressure as the boiler (probably 30 psi) should do. The valve with the yellow tag is not good. The new valve should (well, the code says "shall") be directly connected to the piping served, without any more bends or piping than absolutely necessary. There should be no valves between on any piping associated with it. It should be piped to discharge 6 inches from the floor.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • frankjc
    frankjc Member Posts: 38
    edited September 2020
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    So would something like this let out any hot air or steam that might happen? https://www.supplyhouse.com/Apollo-Valves-1040805-3-4-FNPT-RVW10-535000-BTU-Bronze-Relief-Valve-30-psi?gclid=EAIaIQobChMI8eXN_biH7AIVFI3ICh3m2QqwEAQYASABEgIBqfD_BwE
    and would it just be put in place of the valve with the yellow tag?
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    Yes, it would. But, as I said above, I'm not a bit happy with the way that valve with the yellow tag is located or piped.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • frankjc
    frankjc Member Posts: 38
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    I could install a pipe down, about 6" from the floor. Perhaps a bucket under it.
    Or what if I piped it so it was still fed cold water, but close the hot water out valve which is above the boiler?
  • Jamie Hall
    Jamie Hall Member Posts: 23,452
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    First option is better. That way you won't have to worry about a possible leak in the coil overpressuring your system, but still have a safer discharge should the valve open.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    frankjc
  • ethicalpaul
    ethicalpaul Member Posts: 5,737
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    Congrats on separating your DHW from that nasty inefficient boiler! You’re going to love that Rheem if it’s half as good as mine has been.

    are you going to run it just heat pump mode, or let it decide when to use the resistance heating?
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • MichaelG
    MichaelG Member Posts: 26
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    It's been a few years but I thought I would provide an update on how this went for me. I ended up proceeding with abandoning the tankless coil in place. The inlet and outlet pipes for the coil came out of the coil and went straight up several feet, so i simply cut them off, covered them with a few layers of metal screen, and clamped the screen onto each pipe with a hose clamp. It worked great (I sold the house a year later).

    Just a side note- moving from the tankless coil to the Rheem heat pump HWH was a fantastic choice. I got a great deal on it thanks to the rebate from my electric company, and it was a source of free AC for the lower level all summer. It really brought joy to my heart to tell the oil company they could stop making summer deliveries.

    Thanks for everyone's input on this.
    ethicalpaul