Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

McDonnell & Miller 150SHD low water and pump controller sticking on very occasionally

but very much a drag when it does. twice last season I came in on a no heat call and the pump controller had stuck on and turned this steam system into a hydronic system. but it was once near the beginning of the season - took the cover off the control and put it back without 'fixing anything' and everything was 'fine' even before i set about draining the system. and then it ran 3 months with no problem and did it again at the end of the season, so i checked the weather and shut the boiler down, but i gotta get it ready and raring to go.

It just seems like if the float is leaking the symptom would have cropped up again much more quickly. just checking if anyone has seen this symptom and traced a cause. thanks,

brian

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,263
    I had the same thing happen last year on one with the older mercury switch type. Checked and cleaned and flushed the control and it would still occasionally stick. My coworker had one stick on a different job. We ended up changing both of them to solve the problem but could find nothing wrong with the old controls. I HATE being a parts changer. But both worke without issue after being changed.

    Is yours mercury switch or the newer snap switch??
  • Ken D.
    Ken D. Member Posts: 836
    Have you removed the float from the pumpkin? If there is mud in there, that is the reason for the float sticking. Mud can build up even with routine blowdowns. The linkage could be sticking also. Carefully inspect it. My advice is to replace it. One thing you don't want is that boiler to fire dry. At the very least, the boiler would be ruined. The thing could cause a fire and if some water should be fed into the boiler while red hot a devastating explosion would result with a possible loss of life. A new, reliable control is cheap insurance.
  • GBart
    GBart Member Posts: 746
    ....and at 10 years REPLACE YOUR LWCO'S!!!!!!!!!!!!!!!!!!!!!!!
  • GBart
    GBart Member Posts: 746
    here's a video of what happens when your pump control and LWCO malfunction and people keep running the boiler while thinking about it or waiting for parts



    LWCO's should be pulled apart every year, do yourselves a favor and on new installs or after pulling apart anti seize the bolts, the faces and the gaskets, use hi temp anti seize, they will come right apart next with no fuss, the gaskets will peel off
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,263
    edited October 2018
    @Gbart
    The issues I had were switch issues. Had nothing to do with mud. It's the switch hanging up for no apparent reason on controls that had been cleaned and serviced and all piping flushed and serviced.

    I don't know if @Archibald Tuttle is having the same issue

    if you have this issue some day you won't soon forget it
  • archibald tuttle
    archibald tuttle Member Posts: 818



    Is yours mercury switch or the newer snap switch??

    snap switch, so not the same as the ones you had trouble with. it was indeed due for a cleaning but i have a hard time conceiving that what i found kept the float from rising although i can't really tell if the motion of the float could have placed it low enough to be 'stuck in the mud' i found on the bottom, and of course because it happened quite infrequently, i can't really know this has 'fixed' it, but fingers crossed.

    there are actually two LWCO on this boiler one, is the feeder and initial cutoff and the other is a manual reset. i tested their functionality for shutoff weekly during the season, when flushing, but no question a visit to the interior was warranted, but was mystified by this sporadic stick down.

    thanks all,

    brian

  • GBart
    GBart Member Posts: 746
    Have they ever been pulled apart and how old are they?
  • archibald tuttle
    archibald tuttle Member Posts: 818
    yes, this has been apart. i think the controls are about 15 years old, dating to boiler swap before the building came into our portfolio.
  • GBart
    GBart Member Posts: 746
    edited October 2018
    10 years and replace your LWCO's for most, your particular model states in the manual the following:

    Replace head mechanism every 5 years.
    More frequent replacement may be required when
    severe conditions exist.
    Replacement parts are available from your local
    authorized McDonnell & Miller Distributor.
    The use of parts or components other than those
    manufactured by McDonnell & Miller will void all
    warranties and may affect the units compliance with
    listings or regulating agencies.


    http://dominion.com.mx/fichas/control-de-nivel-mcdonnell-miller-259.pdf
  • archibald tuttle
    archibald tuttle Member Posts: 818
    I see that some folks are looking at replacing controls a decade out and i see your pointing to supporting documentation. this was rebuilt once about 5 years back. With rebuild kits and parts access for cleaning that 10 years seems aggressive to me vs. inspection and maintenance. I understand its a serious protection and just because some work long time beyond doesn't prove when an actual risk of failure to protect not addressable by regular maintenance actually rises noticeably.

    I'm wondering what they really think the failure mode is and whether that 10 years is some combination of marketing and CYA from their point of view since I have never seen contracted boiler maintenance replace these without some symptoms of distress in most residential applications in 40 years watching and participating in the trades in this area.

    That said, from a practicality and precaution approach, I have to check whether there is a tapping at an appropriate level and i can add a probe type LWCO in addition or as replacement. reviewing what folks have had to say on the subject, virtually all LWCO failures they observed (which is to say failures to protect) are associated with the physical float type LWCO. Now this can also be associated with clogging of pipes as well as the device itself, esp. the lower pipe returning to the boiler so water in the LWCO doesn't reliably drop at the rate that boiler water drops.

    On hydronic i'm adding LWCO in tees. If there is not a tapping at the cutout level itself it seems to me that I could create a pipe manifold where the physical LWCO is installed with a tee on the rise at the right level for a probe (and i'd put a horizontal run tee with a hex plug at the bottom of the manifold so i could physically clear that lower pipe annually. suppose i could do the same at the top where i haven't experienced as much build up problem since it is over the typical waterline but a 4 inches but if it were plugged, failure to equalize pressure could cause misindication of level.) I have to pull the brochure on recommended install for whichever I would choose. I'm most familiar with the TACO LTRO243T-1 which is only speced for hot water although TACO has offerings that go steam as well, and the install instructions for those show installation in a pipe with clearances required from the pipe wall. now i imagine that could mean a problem with corrosion although i could use a copper riser for the tee to cut back on that. I know folks like the hydrolevel, i'm not saying which way i would go but i was looking quickly for install notes.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,263
    On hydronic you can stick a probe type in the boiler supply. Just keep it above the top of the boiler it's done all the time. Stick it in a tee or thread o let
  • archibald tuttle
    archibald tuttle Member Posts: 818
    right, that's my common approach. when you say supply do you mean system supply/ feed from boiler, or do you mean supply to boiler, i.e. system return. I'm not sure I have an absolute convention in mind and in the old pump away scenario wonder if it ought to be just on the feed side of the boiler pump (above of course the boiler itself - but i'm not so much thinking of systems that are low on water but that have trapped air . . . this just got me thinking)

    meanwhile, after many blank stares I finally found the info on steam install options and an equalized pipe install is OK which can solve the level choice easily and allows dual install for a separate feeder and LWCO trip although the digital programing and timing should be able to handle this in the same control it still could be desirable where you have a manual cut-off to maintain dual controls with an inch or two of additional margin on the fill control. Hyrdolevel sells wide branch format cast iron tees but i favor a copper rise and tee anyway all of which are acceptable when you get to the fine print as long as clearances are observed. this is for the safeguard 550 commercial but i expect the install scheme would be similar for the 400 residential




  • GBart
    GBart Member Posts: 746
    All the next generation LWCO's with a probe are essentially the same, a stainless steel probe looking for ground ( the water) from a small micro processor.

    I don't like them installed in a pipe on the side of the boiler and neither do inspectors, they should be in the boiler or in the supply piping right above it, in the case of steam they should be right in the boiler.
  • archibald tuttle
    archibald tuttle Member Posts: 818
    GBart said:

    All the next generation LWCO's with a probe are essentially the same, a stainless steel probe looking for ground ( the water) from a small micro processor.

    the principal difference i've identified is actually the processing end not the probe side. the original hydrolevels shut down the boiler periodically after short cycles (i think it was 10 minutes IIRC) so that the water level would settle for reading. their later ones appear to be able to average or process inconsistencies in signal during operation to give a reliable result without doing this. TACO advertises (and I'm not sure but what that is green spray paint on somebody else's box or not . . . ?) particular industry leading capability in this dept.

    I'm open, i.e. asking for , any observations on these developments. none of these new processing approaches have been in place long enough - to my knowledge - to be able to report on the robust decade long operation but i'm thinking some folks have had field experience to report . . .
    GBart said:

    I don't like them installed in a pipe on the side of the boiler and neither do inspectors, they should be in the boiler or in the supply piping right above it, in the case of steam they should be right in the boiler.

    Sure the direct install is the preference. that's all fine and good, unless there isn't a tapping at the right level for install. i can't see why a physical float type in an equalized manifold is preferable to a probe type in a similar arrangement with the exception if one is billing install as maintenance free.

    these aren't even 'maintenance free' installed directly in the boiler. the same kind of literature cautions as accompany the float style in the instance of the probe literature i'm seeing say to remove the probe and clean annually. That is no average homeowner upkeep and at least in your standard residential boiler service I inquire as to whether that is a regular undertaking.

    In addition, if the probe is in a pipe manifold, periodic flushing/cleaning would remain relevant. my intention is for most of the manifold to be copper instead of black pipe. realistically i'll leave the first nipple and cross at the bottom and then use dielectric unions to transition to the copper riser and on the top horizontial to maintain access for flushing and physically cleaning that bottom entry. and then i'll observe some modest additional clearance from adjacent surfaces to the probe beyond the minimum 1/4" specified.

    Bottom line is, if we are going to take the manufacturer's literature seriously, as in pull this control and clean every year or replace this control every 10 years, I question why their installation guidelines should be disregarded as faulty.

    (BTW, while looking at these options, gave both the physical controls a real going over. I definitely could detect a hitch at the top of the float arc on the 63H unrelated to corrosion/sludge built up in the cast iron vessel. relaxing and tuning the connection from the float to the non-immersed fulcrum and a tiny bit of light oil lube and the thing is like brand new., i will confess to not paying enough attention to the non-immersed linkages previously. i'm here to learn, not to preen or belly ache, and I appreciate being schooled. I trust you understand that I respect the preference you express on location for probe style update, but my experience has been that it is not an option on many boilers -- not to mention the question of boilers that place a feeder control above the LWCO that would require two relative closely space tappings at a level appropriate to those intentions. There may be some ability for this brainy processing to detect frothing and waterline as a fill signal vs. lack of water as cutout signal that could, with proven track record, obviate this dual level mounting, but this boiler has a two inch separation in the currently mounted 105S controlling the return pump and the 63H manual reset LWCO which you aren't going to duplicate on the vast majority of boilers without a manifold. - and sometime when i want a real piping challenge, this did not need return pump in the first place if run at vapor pressures -- and I think it was originally piped for gravity return -- but in the wisdom of the folks who did the last boiler replacement around the (recent) turng of the century, it was converted to pumped return. well, that's getting too close to bellyaching and I appreciate a challenge but it ain't happening this season. syonara)
  • archibald tuttle
    archibald tuttle Member Posts: 818
    Murphy gets the last laugh, it wasn't the LWCO after all. The motor relay for the condensate pump is occasionally very lightly welding itself closed with the starting arc. i finally caught it this iteration of the problem. Every other time when i got anywhere near the boiler and touched anything the problem stopped but i very gingerly inspected the LWCO and it was not sending any low water signal but as i pried off the cover to the relay which was getting no current to its coil at the time suddenly released stopping the pump. The points didn't look new when i had glanced at them before but dark corner and i didn't credit the notion that they had been stuck together. Well my LWCOs got a good going over but now its on to finding a simple replacement contactor/relay. You can buy one very inexpensively with tab terminals but, i guess for number of units or whatnot, screw terminals for field wiring are some rarity -- nevermind, god forbid, screw style compression set up for straight stripped wire. of course you can pay 10 times the cost of a relay for a trade box with screw terms, but that seems kinda silly. i gotta go figure what's the proper place to discuss the best source for relays where you can sort easily by connection options. i know i could go cube but standard tabs anyway are as likely to be the failure source for this kind of application as the relay points themselves. the motor draws 8 amps with 20 amp startup (that's tested amperage). that gets to connectors after a while!

    GBart
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,263
    I always oversize the contactors or relays. the price difference is usually minimal and prevents problems
    GBart
  • archibald tuttle
    archibald tuttle Member Posts: 818
    eddy, ebe?

    i want to complain about the lack of a thumbs up in the glyphic selection here. you can't forget about the faces and give us a thumbs up or a thumbs down . . .

    agree on amperage. i got a 40 AMP relay for an 8 amp load which has 20 amp inrush current. one thing i'm lamenting on my other thread desperately seeking contactors is that you can't get a simple single throw version of the heavier ones that are ubiquitous for heavier loads in HVAC equipment itself - e.g. 2 and 3 horse 240 or 208 volt compressors. those as simply too big for a lot of the in situ field enclosures where you might be replacing a relay for a smaller motor. i really like the form factor of one that was recommended but its a 20 amp relay. i'd like to know how they go in the field 15 or 20 years out on the kind of load i'm dealing with which is within spec but without as much wiggle room as the 40amp.

    brian

    GBart