LWCO 67 Switch Troubleshooting

Steam42

I think the switch on my MM 67 LWCO might be bad. For years I've manually fed the steam boiler through the autofeeder because when I bought the house I was told it didn't work correctly. I've recently tried to wire it up to work, and the issue I'm experiencing might be why it was disconnected. I have 24V coming to terminal 2 when the thermostat calls for heat, and there is continuity to Terminal 1. When operating the blow-off while the burner is running, the float drops as expected and the switch clicks and the burner turns off (to me, this is the "down" position and this cuts the power to the boiler and should "start" the autofeeder after a min or so of continuous power). I added the jumper from Terminal 2 to Terminal 3, and Terminal 4 is connected to the autofeeder. The issue is that the LWCO constantly calls for water. In it's "neutral" (center?) position, the switch has continuity between Terminals 3 and 4. My understanding is that this should only occur when the water level is low and the float falls and clicks (e.g. the "down" position of the switch).

I've taken the switch off and tried to operate it manually, and the switch only loses continuity between Terminal 3 and 4 when the switch is clicked "up".

Is there a chance that my float isn't floating high enough? Is the switch supposed to have three positions - up, center, and down?

EBEBRATT-Ed

Float and switch are two position only. Contacts between 1&2 close when the water is above the float and open when the float drops to shut off the burner.

contacts between 3 & 4 close when float drops to turn feeder on.

If the switch is ok the float could be bad (floats can have a pinhole and be partially filled with water). You could have crud in the LWCO body. Switch must be mounted with #1 and #2 at the top. #3&4 on the bottom

Steam42

Thanks for the quick response. I can confirm that the switch is installed with 1/2 at the top. I'll continue to work on it - maybe try putting some more water in the boiler to see if the float level raises. I'll take any other thoughts/comments though!

Steam42

After fiddling with it some more and checking out some YouTube videos on float operation in the 67, I am almost positive that the float is hitting something internal to the LWCO that is preventing it from rising high enough to activate the switch in the "up" position (e.g. power to 1/2 only). Is it possible for the pigtail to be threaded into the LWCO too far and it's making contact with the top of the float/bellows? Or there could be build-up at the top of the LWCO housing. Let me know if anyone has seen this before. Thanks!

109A_5

Hello @Steam42,
Terminals 1 to 2 is one switch, terminals 3 to 4 is an entirely separate switch in the same assembly. There is a subtle difference in float level as when the two different switches change state. There is a point or a narrow water level range where they both should be closed.

Starting with the boiler water level at a normal place;
Terminals 1 to 2 are closed (Burner control, burner enabled)
Terminals 3 to 4 are open (Water feed control, water feeder disabled)

As the water lowers with system use it gets to a point where
Terminals 3 to 4 close to add water so to not interrupt the burner operation. If the water level goes up all is fine. Terminals 3 to 4 then open shutting off the water feeder.

If the water level continues to lower (just a bit, but slightly lower) the
Terminals 1 to 2 are then opened, shutting down the boiler's burner.

If the water level is manually raised once the Burner is cut off, Terminals 1 to 2 close first then with the water level a bit higher Terminals 3 to 4 then open.

I would test the water feeder independently of the M&M 67 by closing the feed call wires.

There are some wiring examples in the Manual.
https://s3.amazonaws.com/s3.supplyhouse.com/manuals/1351003889438/84672_PROD_FILE.pdf

Steam42

Thank you for this info - it appears to confirm my suspicion.  I’m stuck around the orange zone.  The switch allows the burner to continue to operate but continuously calls for water, as the float cannot go any higher (see above post) to get to the condition where it’s only supplying power to 1 (burner) and not 4 (water feeder).  I have not found any issue with the water feeder - it operates as expected when called from terminal 4 (it waits 1 min, then fills for 1 min, etc).

The switch does go into the red zone when I blow off while the burner is running - the float drops enough to cut power to the boiler.

109A_5

Hello @Steam42,

Steam42 said:

After fiddling with it some more and checking out some YouTube videos on float operation in the 67, I am almost positive that the float is hitting something internal to the LWCO that is preventing it from rising high enough to activate the switch in the "up" position (e.g. power to 1/2 only). Is it possible for the pigtail to be threaded into the LWCO too far and it's making contact with the top of the float/bellows? Or there could be build-up at the top of the LWCO housing. Let me know if anyone has seen this before. Thanks!

The float not rising high enough would keep the water feeder constantly feeding water (terminals 3 to 4 closed) if the water feeder is connected to the M&M 67 and if the float level is at that sweet point in the float's travel.
It is possible for the pigtail thread to contact the float but unlikely, the pigtail threads would have to be very long. Your M&M 67 is probably rusty inside and needs cleaning. Others and myself have cleaned out the M&M 67 successfully, not too hard just messy. See this thread (don't miss the videos)
https://forum.heatinghelp.com/discussion/comment/1720459

Fred

I would put my money on the MM67 needing a good clean out/scraping. Rust/debris builds up on the floor of the MM67 body which does not allow the float to fully drop and the side walls can also build up enough crud that the float can rub against the side walls and hang up.

BobC

This kind of problem can be greatly reduced by keeping the boiler water clear with a treatment of some kind. The water in my 9 year old Smith steam boiler is pretty much free of any rust and mung because I've used steam master in it since it was new. All I do is drain it every few years and refill it with fresh water and a tablet of steam master. They don't sell that any more but I have enough to last me the rest of my life, there are other potions that do the same thing by keeping the PH high.

ethicalpaul

Steam42

Last night I removed the float and cleaned the inside of the lwco, as well as the float, bellows, etc.  I do not think the float has any water in it - could hear or feel anything in it.  Reassembled everything with a new (hand-made!) gasket.  Unfortunately, the float still only operates the switch enough so that 1/2 and 3/4 all have continuity (eg the “center” position).  I feel the float is hitting the top of the lwco.  Here are some pictures of inside the lwco (before - rusty, and after - black).  I did blow down a number of times after to rinse out any remaining gunk.

Steam42

Before picture might not have worked.  Here it is

JUGHNE

IDK if it makes much of a difference, but is the LWCO and boiler level?

Steam42

Honestly, I thought about checking that.  The lwco might be slightly off level.  By eyeball maybe 1/8 to 1/4 inch across the body.  I’ll have to check with a level later.  The switch side is the low side.

Chris_L

The float is supposed to hit the top of the LWCO when it is floating and the boiler is up to its normal water line. At least that is what the two of mine do, and they work fine. (I don't have an automatic feeder.)

The only time I have problems is when the LWCO gets gunked up and the top of top of the LWCO starts growing stalactites. (From your "after" photo, it looks like you've taken care of that.) If the bellows gets gunked up enough, it can also prevent the float from rising all the way.

You have to make sure you've installed the float with "up" in the right position. If you've done that, and the float is going as high as the LWCO body allows, I think your problems are probably elsewhere.

109A_5

Hello @Steam42,
When it was apart I would have verified the switch functionality with a Multi-Meter, Ohmmeter or a continuity checker. That way if the switch worked off the LWCO housing and it does not work when mounted you can look for a mechanical issue. As you move the switch actuator through its travel you could hear two clicks. I don't recall if the float can be mounted wrong (or upside-down) in relation to the switch. The switch assembly is labeled "TOP" I believe. There is a adjustment set screw, I have never messed with that, never needed to, not sure what it actually changes. Maybe the change of state of the switch for a given float position or the mechanical differential between the two switches or something else.

If the switch is actually bad, it (only) can be replaced, and appears to be available.
https://www.supplyhouse.com/Mcdonnell-Miller-309100-11-No-11-Switch-Replacement
Black colored body 24 -120 VAC applications Red colored body is for Milli-Volt applications.

Still much more inexpensive and easier than replacing the whole M&M 67 unit.

I made a gasket out of silicone rubber sheeting. Hopefully this gasket does not have the downsides of a paper gasket, making inspection and minor cleaning faster and easier. As far as I know my M&M 67 had never been cleaned since it was new, over 50 years ago, it needed it, I may inspect it annually now.

Nice job cleaning yours.

Fred

What water feeder are you using? Most have some dip switches in them that have to be set based on the type of LWCO you have.

Steam42

@Chris_L - good info that yours hits the top of the housing.  Basically, it seems that mine does that, but it’s not enough travel to make the switch break the continuity between terminals 3/4.  I’m also not sure that the float has a top or bottom - it seems symmetrical to me.  I did clean the float and bellows as well.

@109A_5 - I have tested the switch and can confirm that it does operate in all three positions - up (continuity between 1/2 only), center (continuity between 1/2 and 3/4), and down (continuity between 3/4 only).  It’s the down position that the float/switch never achieves.

@Fred - it’s a UniMatch and the internal switch is set correctly to the MM setting.  I’ve found no issues with the feeder.  It works as expected.  It’s the lwco switch that is always sending a signal for water, no matter what the actual water level is.

I assume the adjustment screws on the switch are used by the manufacturer to adjust the switch for small manufacturing tolerance differences.  I would consider trying to adjust them if we’re out of ideas.

I did check the lwco for how level and it’s not perfect but the small amount it might be out of whack didn’t seem to do anything when I “gently” pulled it/pushed it

Really appreciate everyone’s thoughts.  I’m doing this on my boiler and will be helping a family member’s with theirs so learning is imperative!  

JUGHNE

With the boiler drained down below the LWCO, you can open the blow down valve and push on the float with a stick.
What switch results might you get doing that very slowly?

109A_5

Hello @Steam42,

Steam42 said:

when I bought the house I was told it didn't work correctly.

The M&M 67 may never have worked correctly from the factory. I would agree the float may normally hit the top of the housing. If there is no obvious low spots in the inside top of the housing casting or debris stuck on the top of the float and the bellows will allow enough movement range to trip the switch to open terminals 3 to 4 and the switch otherwise works correctly, I would think the switch assembly is not calibrated correctly.

I have seen different versions of the switch assembly, the calibration method has changed over the years. If you change the calibration of your unit and it has two set screws I would turn them equally. like 1/4 turn in and a 1/4 turn out on the other screw. This would maintain the dead band where both switches are closed.

On mine it looks to me like when the switch actuator plunger is pushed in (towards the switch) for the switch to open. So in your case (if you have set screws that directly push on the switch plunger) I would think the top set screw for terminals 1 and 2 would have to go out (away from the switch) and the bottom set screw for terminals 3 and 4 would have to go in (towards the switch). This would have to be verified on your unit.

Mine unit is old and the adjustment screws are different than the picture, they are on the side of the seesaw part.

109A_5

Hello @Steam42,
I could not resist some tinkering on this one. On my M&M 67 switch assembly the dead band where both switches are closed, each end of the Seesaw piece is almost perfectly equal-distant from the switch housing.

The float does contact the top of the housing where my water level presently is, I can hear and feel it when moving the float by gently pushing up and down on the roller with the switch assembly removed.

With the switch assembly attached the Seesaw is moved significantly to push on the lower switch plunger. Opening the switch to the terminals 3 and 4.

Edit: My Seesaw part is actually three pieces held to together with two screws, one screw on each side. On the newer style I would consider the part of the Set screws that touches the switch plungers as part of the Seesaw for reference purposes.

Steam42

We’re on to something.  My switch looks like the one pictured, with the screws in that configuration.  I went down and tried something - see attached picture.  I used a flat head screwdriver to put a little pressure against the black plastic body of the switch, in the direction away from the float (blue arrows).  I immediately heard a “click!”.  Got my tester out - when it clicks, 3/4 lose continuity!  When I look at the rivet head (red arrow) the rivet moves back maybe 1/32 of an inch.  I think this is the issue!  So either the switch has loosened over time, or maybe never worked correctly.  My thought is to install some kind of shim, etc. to remove the play.

I’ll report back when I have more to share.  You all have been so helpful!

NOTE: when the switch “clicks” upon the screwdriver pressure, 1/2 maintain continuity as expected (burner would still run).

109A_5

My switch assembly does not have rivets. I suspect on mine if I remove all four of the terminal screws that cover would come off and it would all fly apart. The two half's of the switch housing are snug together on mine.

I don't think this gap should be there. See picture.

109A_5

Looking at an on-line image of a M&M 67 switch it does not look like a rivet. It looks like a tamper proof screw head. It can be screwed in but not removed. If yours is the same can you just snug it up ?

I found another on-line image that looks like a pin that was peened over in a plus or cross pattern.

Steam42

I’ll take a look later.  It may not be a rivet - could be a tamperproof screw.

But that’s exactly the gap that is removed when I pushed it with the screwdriver.  That little amount is all it took to open the switch.

Steam42

Well, I’m happy to report I have a fully functioning LWCO, switch, and auto feeder.  All are now working as expected.

I ended up taking the switch apart.  The “rivets” were actually round-headed metal pins that had back-cuts on them (similar to a plastic drywall anchor).  The pin gets pushed into the switch cover and those back-cuts are supposed to prevent them from pulling out.  Newer ones probably went to screws for a tighter, longer-lasting hold.

The switch assembly kinda reminded me of a old car with points - each side of the switch has a pad that makes contact.  I wasn’t getting continuity so like you would with points, I used some very very fine Emory paper and ran it across each side a couple times.  Cleaned up perfectly and now the switch was operating on the bench perfectly.

I reinstalled it and determined the lower switch for the feeder needed adjustment.  With the float at the top of the LWCO, the feeder switch (3/4) was staying closed, meaning the feeder would run constantly.  I ended up adjusting the screw about 1/2 turn (required a very small Allen key/bit) in, which worked perfectly.  Now, with the float at the top of the LWCO, the feeder switch is open.

I went through the full operation a number of times (blow down LWCO, have burner turn off, have water return from boiler and turn the boiler back on, no feeder) and then with the low water condition where the burner won’t turn back on and the call for water is made.

I think I’m done with this project - thanks to all that helped along the way.  If you have questions I’d be happy to try to answer them.  I would not have thought the Emory paper step would be needed - maybe that tip helps someone else out in the future.

Switch closed (neutral or “center” state)

Switch open (pushing with finger).  You can see the two circular pads that come in contact when the switch is closed.  These pads are what I cleaned with the Emory paper:

Screw adjustment - this is before adjustment.  The bottom screw got turned in about 1/2 turn, extended the screw more to the left, similar to the top screw.:

109A_5

Hello @Steam42,
Excellent !!! Thanks for the pictures. I would think you would have not needed to clean the contacts since continuity of terminals 3 to 4 all the time was the original problem and the burner worked too. An inexpensive repair with a bit of tinkering.

pedmec

your contact points were probably stuck together. That could explain why the water feeder was continuously calling. Disassembling allow the separation and cleaning might prevent further problems. You see if the contact pints are sticking if you closely at them as they get deformed. Switches like these are snap acting to prevent arcing as the contact points get close together. Congratulations

Steam42

The contact points only fouled during disassembly - I’m thinking maybe the grinding I did on those rivets got drawn to the contacts (assuming they’re magnetized?).

I don’t think the contacts were ever stuck together, as the switch would work when manually operated (before opening it and then after opening it and cleaning).  I think the lower screw needed to be adjusted in addition to the housing being tightened up so there wasn’t so much play in the switch.

BobC

I remember a very old Honeywell keystone thermostat (1920's) with a bimetal strip instead of a mercury bulb would need it's contacts cleaned about once a year. I always used a fresh dollar bill because it was abrasive enough to clean the contacts without wearing anything down.

Bob

Big Ed_4

Since the low water cut off is a safety control , I would never play around with it except flushing it . Either replace the complete float assemble , MM6667 or replace the complete MM67 .

If you ever have problem with no heat upstairs and the basement is hot as hell , Back out and shut off the switch on top of the stairs . Leave the house for a good 24 hours before returning with a tech .

reggi

BobC said:

I remember a very old Honeywell keystone thermostat (1920's) with a bimetal strip instead of a mercury bulb would need it's contacts cleaned about once a year. I always used a fresh dollar bill because it was abrasive enough to clean the contacts without wearing anything down. Bob

They don't make dollar bills like they did 100 years ago.... what would you use now 😊

neilc

guys on utube swear by cnotes

109A_5

reggi said:

what would you use now 😊

A contact burnishing tool.
https://vetco.net/products/contact-burnishing-tool-small/gc-9337
https://vetco.net/products/contact-burnishing-tool-large

BobC

Crane produces the paper stock used to print US currency since 1879, it's made of 25% linen and 75% cotton. I know they added some colored synthetic threads to new notes a while ago but other than that I believe the currency paper has remained the same for a long time. So despite it's shrinking worth the dollar's paper feel has stayed pretty constant.

I've had and used burnishing tools for decades but it I don't have one with me a crisp bill usually works. The tape recorders made by Revox in the early 70's had 4 plug in relays that controlled the three motors and solenoid. The contacts on those 4 pole relays would tarnish over time because of air pollution. I had to replace them with relays that had heavily gold plated contacts so i wouldn't have to clean the contacts every few months.

ethicalpaul

Air pollution!? Did you have a coal plant in your house?