LWCO w/a Knight Wall Hung

MikeyB

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

Jean-David Beyer

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

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

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

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

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

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

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

lwco

Bump

PaulR

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

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

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

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

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

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

MikeyB

lwco

Thanks Paul and ME, good point about the cross tee & air vent, much appreciated guys

Nathan_6

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

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

lwco

Great pic Nathan, thanks for your input