Low water cut off

eltin

I have been searching videos and all over the internet on the function of a LWCO, and I'm a bit lost. I have a Pennco series 1604HSID that was installed about 7 years ago. The LWCO was changed out what appeared to be a used Mc and Miller 67. I have been told when the water goes low and calls for water the flame is supposed to be out until it refills and the lights up again. A couple of times it has done it when I initially started back up the boiler this season. Currently while the flame is still lit and water appears to be low, It will call for water and be refilled. I think that the water goes way to low in the sight glass, before it calls for water. I'd say less then a 1/2". Is this normal or do I need a new LWCO, and if so what would be an appropriate model for this boiler. Thanks

Paul S_3

I believe as the water level drops on the #67 it sends power to the feeder first with the burner still lit......if the water level drops even lower it will interrupt power to the burner .....

Fred

The MM#67 is a float type LWCO and it should be blown down weekly during the heating season. Flush water out of it until the water runs clear, usually a quart to a half gallon. They should be taken apart and the float chamber scraped out annually and MM recommends they be replaced every ten years. To test the unit, fire the boiler up and open the valve on the MM#67. in about two to four seconds, the boiler burner should shut down. If it does, it is working properly. If the boiler does not shut down, it needs to be serviced. There could be enough build up in the float chamber that the float is hung up on the the side walls of the chamber or the float itself could have a lead and be water logged. You can order new gaskets for it, when you open it up, both the bottom blow down valve and the electrical box end. You will need those gaskets to put the unit back together. You can also order a new float, switch unit, blow down valve, etc. Ebay usually has a good listing of new units and parts. Just search on McDonnell Miller #67. Be careful when you are testing the unit and while the boiler is running as the boiler water may be hot.
You can replace this unit with a probe type LWCO which will eliminate the need for weekly blow downs but you will need an appropriate boiler tapping for the probe to mount. which can be a problem on some older boilers and if there is a tapping available, getting the plug out can also be a challenge..

eltin

Ok. It does cut the power of when the valve is open. I'm not sure why it was suggested that I replace it and doubt that it was ever was taken apart. I try to do blow downs frequently until I see clear water. I'm just curious about these thing because I've had some experience with so called plumbers in the past and realized that I have to familiarize myself with terminology and parts so I wouldn't be taken for a ride.
I wanted to also add that I have read here that cut in for the pressuretrol is 0.5 and the cut out, while dial should be at 1. I asked this because I noticed the cut in set at 3.

Fred

Paul S said:

I believe as the water level drops on the #67 it sends power to the feeder first with the burner still lit......if the water level drops even lower it will interrupt power to the burner .....

@Paul S It's not that sophistocated. It is all mechanical operation. The end of the float unit has an upper and lower contact lever on it. The float is either riding on top of the water and holding the safety circuit closed or, if the water get low enough that the float drops away from the upper contacts (Safety circuit) the lower lever makes contact with the auto water feed circuit, closing it to trip the feed. The burner goes off as soon as the float drops away from the upper (Safety circuit) contacts.

Jamie Hall

First, on pressure -- the cut in should be set between 0.5 and 0.75. Do not set it right down at 0.5; it can come apart which isn't good.

On the McDonnell Miller -- it should feed first, as the level drops. If the level drops further, it should kill the burner. The reason it is set up that way is to avoid killing the burner on momentary dips, and giving the feeder a chance to feed.

eltin

I have to correct myself, I released the valve and the water was emptied from the sight glass but the burners were still firing. I took the power off because I didn't want to do any damage. Another observation that I have notice is that if the water is below the cut off point, and I turn the switch on to the boiler the flame will indeed light for about 45 seconds until the feeder fills with water. Is this normal as well ?

eltin

So the cut in pressure is indeed wrong, and the cut out should be at 1. Am I correct ?

Fred

eltin said:

I have to correct myself, I released the valve and the water was emptied from the sight glass but the burners were still firing. I took the power off because I didn't want to do any damage. Another observation that I have notice is that if the water is below the cut off point, and I turn the switch on to the boiler the flame will indeed light for about 45 seconds until the feeder fills with water. Is this normal as well ?

Because the MM #67 is attached to the bottom pipe of the gauge glass with a Tee, when you open the valve on the #67, it will drain the sight glass but that is not an indication of how much water is in the boiler or in the float chamber of the #67 at that time. Do the test I suggested, with the boiler running and the feed supply valve shut off during the test. If the boiler does not shut down in a matter of seconds, the #67 needs service.
@Paul S and @Jamie Hall seem to think the MM #67 will trigger the auto water feed before shutting down the burner. That's not the way mine is set up or operated, if I recall correctly and I don't see how that could happen with the way the switch levers (arms) are mounted on the end of the float. The float is either up or down, Up completing the safety circuit Down, completing the feed circuit. I don't recall any way those arms could both make contact at the same time. At least not on mine. I'd test and verify that but my MM #101 auto feeder failed a couple years ago and I took it off because I always had the water supply to it shut off anyway so I could manually check and add water if needed.

Abracadabra

the 67, and all MM LWCOs i've used have 2 relays. 4 terminals. When properly connected, when the water level drops, terminals 3&4 make and should power the water feeder, if water level continues to drop further 1&2 break, shutting off the burner.

I'd look for the schematic, but it's been a long day.

Fred

Abracadabra said:

the 67, and all MM LWCOs i've used have 2 relays. 4 terminals. When properly connected, when the water level drops, terminals 3&4 make and should power the water feeder, if water level continues to drop further 1&2 break, shutting off the burner.

I'd look for the schematic, but it's been a long day.

You guys can't all be wrong! I stand corrected!

eltin

I have tried it until no more water was coming out of the LWCO. I'd say about 10 to 20 seconds, and the flame hasn't cut off

Abracadabra

Your LWCO may need cleaning or it has not been wired properly to shutoff the burner.

eltin

It was working fine last week, after it went in. I've watch them drain it 5 times in a row and the flame would go out. Water feed would feed then the flame on.

nicholas bonham-carter

I had a problem with my MM 67, in that the outlet pipe to the bucket was partially blocked, and would not flow enough water to empty the float chamber, and shut down the burners. New pipes fixed the problem.--NBC

eltin

Yes, actually, water is dripping from it in the closed valve position

Fred

I would say the LWCO needs to be taken apart and given a good cleaning. It sounds like the float sticks in the up position. Tap the unit on the side and see if the float /shut-off works again. With the LWCO valve open, it shouldn't stop draining water until the boiler is almost empty.

eltin

Tried tapping it with a rubber mallet, and it still wont cut off. However, it would call for water while its running.

Fred

eltin said:

Tried tapping it with a rubber mallet, and it still wont cut off. However, it would call for water while its running.

It needs a very good cleaning. The rust/crud buildup on the side walls and/or bottom won't let the float drop enough to shut the burner down.

STEAM DOCTOR

@Fred. Goggle McDonnell Miller 11mv (that's the micro switch for the 67). It's clear from the manual that 3 and 4 will close before 1 and 2 open. I also thought like you until recently

Fred

STEAM DOCTOR said:

@Fred. Goggle McDonnell Miller 11mv (that's the micro switch for the 67). It's clear from the manual that 3 and 4 will close before 1 and 2 open. I also thought like you until recently

Thanks @STEAM DOCTOR .

eltin

I have another question. I have been reading about main vents. And I realize that there are none here. Should I be worried ? The main run is about 40 ft before it elbows to the return. How ever right after the elbow to the return there is a little vent on it

Fred

Post a picture of that vent. Good Main venting will help to push the air out of the mains quickly so that steam can fill that main and begin to flow to the radiators. Poor venting waste fuel and makes for longer than necessary heat cycles. A 40 ft main could use a BigMouth vent from Barnes and Jones, available through Amazon. See below:
https://www.amazon.com/Barnes-Jones-Big-Mouth-Vent/dp/B01F26P13C/ref=sr_1_fkmr1_1?ie=UTF8&qid=1478713415&sr=8-1-fkmr1&keywords=Barnes+and+Jones++Bigmouth+vent

Jamie Hall

eltin said:

I have another question. I have been reading about main vents. And I realize that there are none here. Should I be worried ? The main run is about 40 ft before it elbows to the return. How ever right after the elbow to the return there is a little vent on it

Eh? Is that a wet return or a dry return? If it is a dry return, is there a trap to keep steam from getting into it?

eltin

eltin

Trying to upload the actual vent but for some reason it keeps failing

eltin

<a href="http://s1255.photobucket.com/user/jose06dhr/media/2016-11-09 13.52.21_zpsijcmdksh.jpg.html" target="_blank"><img src="http://i1255.photobucket.com/albums/hh629/jose06dhr/2016-11-09 13.52.21_zpsijcmdksh.jpg" border="0" alt=" photo 2016-11-09 13.52.21_zpsijcmdksh.jpg"/></a>

Fred

That vent is way to small for a main. Your 40' main would benefit a lot from a Bigmouth buth it is very difficult to see how it is mounted and to get a perspective of where it is mounted. It looks like it is actually below the main/dry return. If so, it needs to be above the main/dry return and needs a 3/4" connection.

eltin

yes it off the return thats in copper, any idea as to how i can fix it ?

eltin

eltin

Jamie Hall

If that really is a dry return, I still want to know how steam is kept out of it. If it isn't, you have more problems than just a ridiculously undersized vent.

ChrisJ

Jamie Hall said:

If that really is a dry return, I still want to know how steam is kept out of it. If it isn't, you have more problems than just a ridiculously undersized vent.

Plenty of dry returns fill with steam.
Why are you concerned about this? As long as it drops down below the water line before connecting to another dry return it's fine.

Fred

Looks like if you take that vent and that bushing out of that copper fitting, a BigMouth should screw right on there.
@Jamie Hall it a one pipe steam system with the dry return being an extension off of the end of the main, probably running back to the boiler area where it drops down into the wet return.

Jamie Hall

ChrisJ said:

Jamie Hall said:

If that really is a dry return, I still want to know how steam is kept out of it. If it isn't, you have more problems than just a ridiculously undersized vent.

Plenty of dry returns fill with steam.
Why are you concerned about this? As long as it drops down below the water line before connecting to another dry return it's fine.

This is true -- but if there is another radiator hooked into it... it's a matter of semantics. I tend to call a pipe serving as the outlet for a single radiator, going eventually to a wet return, a drip -- and, of course, it does have to be vented if it does that.

eltin

Yes, that is the return that leads toward the ground and in to the Hartford loop. So a big mouth on this end would work? What about the main?

eltin

That fitting appears to be a 1/ 2" female adapter as well, I thought it was 3/4"

Fred

eltin said:

That fitting appears to be a 1/ 2" female adapter as well, I thought it was 3/4"

Get a short (2" 1/2 inch nillpe to put in that female connector, then put a 1/2" X 3/4" coupling on top of it and then mount the Bigmouth. A 1/2" pipe has more than enough venting capacity for the Bigmouth.

Fred

eltin said:

Yes, that is the return that leads toward the ground and in to the Hartford loop. So a big mouth on this end would work? What about the main?

That dry return is actually at the end of the main. The bigmouth will vent the main.

eltin

Ok, and it is fine to be installed at that height? I believe someone mentioned it should be mounted higher

Fred

Get it as high as you can. If you have the room, use a 4" or 6" nipple instead of the 2" I suggested.