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Automatic Water Feeder shuts off power at low water? Plumber says it's the thermostat

lowwaterlowwater Member Posts: 40
Here's the situation. Hope you can help me. I have a:

-Honeywell YTHX9421R5010 Prestige IAQ Comfort System Kit (Includes Thermostat, EIM, Portable Comfort Control, Outdoor Sensor)

- Burnham SIN5LNC gas steam boiler

- McDonnell low water cut off 24 v.a.c switch PSE-802

We have a manual water feeder before, and everything was working fine. Note that when the boiler ran out of hot water, the water cut off switch would cut off power to the thermostat (not sure if that's normal, but it's part of the problem below).

Our plumber installed a VXT-24 automatic water feeder switch. The problem is that when the boiler runs out of water, the power gets cut off, including to the VXT which is connected to the McDonell, so the boiler doesn't get refilled.

Our plumber is convinced the Honeywell is the root cause of the problems (he hasn't seen this type of thermostat before), but I'm not so sure. Why can't the VXT get it's power from the transformer directly, instead of getting it from the McDonell cut off switch? Does it makes sense the thermostat gets it power cut off when the boiler runs out of water?

Right now we're at a standstill since the plumber doesn't want to deal with it until we install a normal thermostat.

FYI - EIM connectors used: R,C to thermostat, W1, R, C to boiler.

PSE-802 to VXT: N (white), H (Red).

Edit: I have done some more research. Shouldn't there be a 3rd, feed, cable from the PSE-802 to the VXT?


Thank you,



  • ZmanZman Member Posts: 3,479

    The t-stat should be hooked to the isolated thermostat relay.

    The Low water cut off should be wired in series with the other safety switches.

    They should not impact each other.

    Beyond that, the fill valve should be tied to the LWCO per the manual and everything should be fine.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • lowwaterlowwater Member Posts: 40

    Carl... In my plain, non plumber English are you saying that the

    thermostat cannot affect the feeder? Is it normal that the thermostat

    get's shut off when when the unit runs out of water? How does the wiring

    look to you (see above)? Thanks!
  • ZmanZman Member Posts: 3,479
    edited April 2013

    I am assuming that this is the correct manual for your boiler

    If so the t-stat should always be powered regardless of the LWCO. The boiler will not fire if the LWCO is open.

    Can you take pictures and make a drawing of your setup?

    It sounds like the LWCO it powering off everything and as you said causing the auto fill to not work.

    Yes there should be 3 wires.

    It looks like the feeder should be wired like the drawing labled

    PS-800 Series


    It is hard to tell because the manufacture assumes no one knows how to read schematics so they don't print them.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SteamheadSteamhead Member Posts: 11,337
    The Burnham Independence boilers

    have a relay which the thermostat operates to energize the 24V circuit that operates the gas valve. it should not affect the LWCO or water feeder. I think someone has some wires crossed.
    All Steamed Up, Inc.
    "Reducing our country's energy consumption, one system at a time"
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Baltimore, MD (USA) and consulting anywhere.
  • Jamie HallJamie Hall Member Posts: 6,660
    There is no way

    that thing is wired correctly.  Nor is there any way that the problem is the thermostat; plumbers are not always the best electricians (I would note that electricians are frequently lousy plumbers; it goes both ways).

    A thermostat is a switch which responds to temperature -- that's true whether it's a T87 or a Nest or anything in between.

    Get the wiring straightened out.  Shouldn't be that hard...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • lowwaterlowwater Member Posts: 40

    All I appreciate the feedback and help! Here's some information:


    water feeder:

    cut off:




    water feeder to cut off: N (white), H [jumper to C] (Red).

    24vac transformer:

    Yellow to C EIN, Boiler

    Blue -> Boiler

    White -> Boiler

    Black -> Boiler

    Boiler white -> W1 EIN

    Boiler Red -> R EIN

    The thermostat is powered from the EIN

    Note: the EIN is the thermostat control unit
  • ZmanZman Member Posts: 3,479
    One line?

    Any chance you could do a simple one line drawing? Just a simple hand drawn showing the devices and how they are connected would be fine. At first glance it looks like you are short a common somewhere. It makes my head hurt without a drawing.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icesailoricesailor Member Posts: 7,265
    Basic Boiler Control Wiring:

    The "Plumber" doesn't understand basic boiler control wiring.

    If he doesn't understand how it works, he needs to stop futzing and trying to DX control wiring because he clearly doesn't know the rats front from the back.

    You need someone else that knows how it is supposed to work. The thermostat is nor normally wired into the safety control circuit. I say it that way because there may be some circumstance that I am not aware of. The Thermostat tells the burner to start. The safety control circuits must all be closed for the burner to start. The "Plumber" should be able to show you how the thermostat is causing the problem. Not just make some empirical statement that through FM, the burner won't start. It's something else. Experience will lead the way. The "Plumber" needs more experience.
  • lowwaterlowwater Member Posts: 40

    Thanks all for the help. Please note that I'm not a professional (neither plumber nor electrician), so bear with me :)

    Uploaded is the diagram to the very best of my knowledge. I am not sure if it's 100% correct or labeled correctly, but it looks about right. The most tricky part is the splicer (also found in the pictures). I also noticed that the orange cable has a grey jumper cables.

    So the question is: why does the when the water cut off gets triggered, all the power to both the water feeder and EIN/thermostat also gets cut off?
  • ZmanZman Member Posts: 3,479

    It looks like your thermostat is connected to the boiler incorrectly. Are there terminals on the boiler that are not being used? Perhaps labeled "TT"  or "R1 W1" ?  You also seem to have some incorrect wiringl between the LWCO and the feeder.

    The problem is once you find something wired this far off, who knows what else they screwed up. I think you should use this info to help find a professional who is qualified to fix it. Once someone has reconfigured the safety circuit, you need to be positive it is fixed correctly. There is a potential that the boiler could fire with a closed damper or that another safety has been inadvertently bypassed.

    I think it is time to get someone to look at it that understands controls.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • lowwaterlowwater Member Posts: 40

    I appreciate all the help. Let me try to describe the items:

    - Splicer: a plastic electricity splicer where a bunch of cable come in one side, and go out another

    - PSI box: I believe this is called a Honeywell pressuretrol

    - Boiler valve: cables that are running down and inside the boiler. I believe this is might lead to the ignition system (I mistakenly called it a valve). Hope this helps.
  • lowwaterlowwater Member Posts: 40

    Carl... Who would be most qualified to look into this? Apparently not a plumber? An electrician? Do they know boilers?
  • ZmanZman Member Posts: 3,479
    In a nutshell...

    The t-stat should be connected to the boiler's isolated t-stat relay. Yours looks like it is wired into the boilers safety circuit.

    When the LWCO detects low water it should disable the boiler's ability to fire (the t-stats should be unaffected). It should then signal the water feeder to add water. Once the water is at  the correct level, the lwco should read this and the  boiler should fire.By your drawing it looks like this is wired incorrectly.

    My concern about trying to diagnose and repair this via the internet is that your boiler has been visited by at least one knucklehead. Knuckleheads don't know much about controls. They will just keep moving wires around until it works. By "works" I mean the boiler will get hot and you will stop calling them to fix it.

    Any good heating company should have folks that understand how these systems work. They should be able to make sure the boiler is wired according to the diagram in the manual and that it is safe to operate. I know some great electricians and have yet to find one that wants to look at boiler controls. Go figure.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • lowwaterlowwater Member Posts: 40
    Thank you

    Thank you all for responding. Much appreciated. 
  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    Where is the boiler?

    There are several contractors in the find a contractor section above that can find the issue and fix it .
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Jamie HallJamie Hall Member Posts: 6,660
    I do hope,

    lowwater, that you have gathered at least one thing from this thread:  your controls are completely mis-wired.  I really can't answer your particular question -- why does the power shut off at low water? -- from looking at your diagram (but thank you for the diagram!), as some of the internals are not completely clear.

    However, that doesn't stop me from saying -- quite firmly -- that I don't think, from the look of it, that there is one single correct circuit in the whole thing except for the two wires from the thermostat to the thermostat EIN.  Those are probably right...

    I would suggest that you rip out all the wiring (except those two wires) and start all over again with the parts manuals to hand.  If you are good at electricity, you might be able to do this yourself.  Otherwise, do yourself a favour and take Charles' suggestion: find a good steam boiler man in your area and let him straighten it out.

    It isn't rocket science, but it does have to be done properly.

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
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