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LWCO w/a Knight Wall Hung

MikeyB
MikeyB Member Posts: 696
With both supply and return connections on a Knight WB-080 on the bottom of the boiler what is the best location for a low water cut off? I know Lochinvar supplies a probe type that is installed in a tee along with the pressure relief valve on the top of the boiler (sold separately), but if one would want to install another type of lwco where would be the best location? thanks guys

Comments

  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    edited September 2009
    LWCO location

    My W-M Ultra 3 claims it does not need an LWCO because its control board can detect that condition. They caution to check local codes because some codes do not accept their statement.

    The Ultra 3 can be piped from above or below. They say "install it in a T in the supply piping above the boiler." Actually, my contractor installed it in the return because the one in the supply had the pressure relief valve in it.



    McDonnell & Miller who make my LWCO say if you boiler has tappings for an LWCO, use one that is above the minimum safe water level. If no tapping is provided, install the probe in a header or riser pipe above the boiler.
  • MikeyB
    MikeyB Member Posts: 696
    LWCO

    The difference between the Ultra is that is sits on the floor and you can install the lwco on the top, but the Knight model I'm talking about is a wall hung and the connections are on the bottom of the unit, I'm not sure if you should install a lwco on the bottom of a wall hung,I have heard of guys placing the lwco and and running the S&R piping above the top of the boiler, this is limited of course to ceiling height and field conditions, if I was looking to install a floor mounted Knight , I would place it right above the boiler, but with the wall hung its a little different, all boilers should have a lwco especially if there is radiation below the boiler
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Ultra boilers can be wall hung.

    That is why the make it possible to run all the plumbing in from the bottom if you wish.



    If you run the piping in from below, you must still put the pressure relief valve on top, and it would not make sense to run the LWCO below the minimum water line, so it also should go on top. It would seem to me that the same would apply for any other boiler as well.
  • Unknown
    edited September 2009
    Pretty simple,,,

    LW means low water,,, NOT pressure.

    CO means fuel supply cut-off.

    Since NO boiler HX should be subject to dry-firing, the logical position is above the unit.
  • MikeyB
    MikeyB Member Posts: 696
    lwco

    Understood Dave, but what is the best way to run the S&R lines, if I install the lwco on the return piping i will have to loop the piping above the top of the boiler and then return it back down to the bottom end to make my system connections,  this way the lwco remains above the boiler? the supply and return mains will be under the boiler. It might be easier and less labor if I go with the lwco probe that Lochinvar can supply that goes in a tee between the relief valve and the top of the boiler, thanks guys
  • PaulR
    PaulR Member Posts: 25
    edited September 2009
    One location option

    Here is one location option.  Obviously, there is no scale in this JPEG.  Is your system loop above the boiler?  Height is slightly exagerated for clarity.

    Paul
  • MikeyB
    MikeyB Member Posts: 696
    edited September 2009
    lwco

    Thanks again Paul, that was one option i was looking at, but I might have to keep the system loop  from the mid point of the boiler or closer to the bottom, I do not have alot of head room to work with, would you have another drawing that would show what I am talking about? thanks again
  • MikeyB
    MikeyB Member Posts: 696
    lwco

    Bump
  • PaulR
    PaulR Member Posts: 25
    edited October 2009
    LWCO Location

    I looked at the Manual for McDonell-Miller LWCO's and it stated that the probe needed to be installed above the minimum safe water line as determined by the boiler manufacturer. 

    I looked at the Knight piping recommendations and it just says that a LWCO may be required when boiler is piped above the radiation level, but not give a specific location.

    Here is a pic of an alternate location that I would consider.  Use another tee as a 90 on the lower end of the system loop.  It is still the lowest part of the system piping as opposed to the boiler piping.

    You can always email Lochinvar tech, they're a pretty sharp group.

    Paul
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Where is the top of the boiler heat exchanger in the diagram?

    I would think you would want the LWCO at least as high in the system as the lowest height the water must be in the boiler. I do not know that boiler at all, but if it is anything like mine (W-M Ultra 3) you would want the LWCO at least as high as very near the top of the box the boiler is in; i.e., in your diagram it appears too low.



    I do not suppose your diagram is meant to be to scale, but let us suppose it is. In that case, for minimum change, I would move the LWCO to the top pipe, where the water feed and the air extractor are.



    I am not a professional, but am I missing something?
  • MikeyB
    MikeyB Member Posts: 696
    edited October 2009
    lwco

    Thanks again Paul, I truly appreciate it, I have been in touch w/Knights Tech dept, very helpful, they had sent me the lit on the lwco they supply at a separate cost w/the probe a while back, the one that will screw into the bull of a tee and the pressure relief will be installed on the top run of that same tee (on the top of the boiler), I think that lwco will cost alot of bucks, so I was looking for another alternative and I know M&M's model RB-24L comes w/ a molex connector to fit in Knights control board. And was looking for a good location to install this lwco. Also if I decide to use a Boiler Buddy buffer tank I might be able to install the lwco off the top tapping to give me the height above the top of the boiler. Thanks again for your help
  • MikeyB
    MikeyB Member Posts: 696
    LWCO

    Just heard back from the technical Dept at Lochinvar they say you can unscrew the relief valve from the top of the boiler and install a Tee on the nipple, screw the lwco in the bull  of the tee and reinstall the relief valve on the top of the tee.
  • Paul Pollets
    Paul Pollets Member Posts: 3,431
    LWCO location

    That's what we do with the Vitodens wall-hung appliances.  FYI: most codes do not allow a valve between the LWCO and the boiler.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Nuisance lock outs...

    Unless the relief valve is done with a cross, and that cross is vented with an auto vent, you can expect to get some nuisance lockouts due to air accumulating at that point.



    As for isolation valves around the LWCO, on bowl and float type LWCO's, isolation valves are required, to allow the boiler inspector the opportunity to test the LWCO without having to drain the whole system. I told the AHJ that it was a disaster waiting to happen, but to no avail. They (isolation cocks) are still required.



    As for preferred location, I like the first drawing that Paul Rohr provided, with the LWCO on the main, above the crown of the appliance being protected.



    FWIW, did you know that most probe type LWCO manufacturers recommend complete replacement every so often?



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • MikeyB
    MikeyB Member Posts: 696
    lwco

    Thanks Paul and ME, good point about the cross tee & air vent, much appreciated guys
  • Nathan_6
    Nathan_6 Member Posts: 40
    If you cannot find a cross

    If you cannot find a cross at your supply house you can also pipe in the LWCO like this.
  • rich pickering
    rich pickering Member Posts: 277
    lwco isolation

    Mark, use 3-way ball valves.  Shut off valves and drain just the water in the lwco column, lwco is off boiler won't fire. 
  • MikeyB
    MikeyB Member Posts: 696
    lwco

    Great pic Nathan, thanks for your input
This discussion has been closed.