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White-Rodgers spdt 11D31 question

FredH Member Posts: 18
Can a single pole double throw switch be used to control both line and low voltage.

Is there a potential issue with line voltage and 24v on the same common.

I guess I am more concerned with the line voltage toasting 24 volt if both circuits are energized at same time than a 24v back current on the 120v side. I  have a good knowledge of electrical wiring but never considered this before.

I want to use switch as a 24 v  low lim and line voltage circulator cutout



  • Tim McElwain
    Tim McElwain Member Posts: 4,446
    The answer is

    no. The two voltages can't be connected to the common on the SPDT switch. What exactly are you trying to do? A little more information would be helpful.

    Typically the SPDT aquastat controls use R to B normally closed for a low limit to operate the burner. Then when R to B breaks R to W makes and is used to operate a low voltage relay to bring in the circulator. The circulator however does not want to come on until there is a call for heat from the thermostat. So R to W should be wired through the relay in series with the call for heat from the thermostat.
  • FredH
    FredH Member Posts: 18
    White Rodgers Question

    Currently it is used as a line voltage cutout for three circulators.

    It was set at 120Deg with closed differential.

     I think the reason it is so low was was because return water is sometimes  close to room temp on call for heat in AM and system would hang if it was a still few degrees above the hi lim differential. Call for heat no circulator or burner.

    Just realized that old  adjustable American Standard CA-666dt in the tankless well was never breaking( took it out and lubricated and tested  and does not break on rise. It was estentially acting as a TT jump and boiler was cycling between hi lim and differential.

    Disconnected and now  burner and circs come on when call for heat and shut off when call is stisfied. Occasionally will run to high lim.

    Hoping to use the SPDT as a low lim and circulator control.

    Each circulator has its own thermostat and relay. Not sure if it is possible to put this in series between 3 t-stats and 3 relays.

    You did confirm what I suspected. Now if it was a DPDT It would work
  • Tim McElwain
    Tim McElwain Member Posts: 4,446
    Or DPST

    will work as you can have 24 volts on one leg and 120 volts on the other leg.
  • FredH
    FredH Member Posts: 18
    what about buying a White-Rogers 11d18-1?

    Reletively inexpensive (about $65) and will serve as inexpensive  replacement low limit control on tankless well. Opens on rise and has an adjustable differential.

    Line voltage to 3 circulators would remain on its own controller. May not be

    the best way but can not figure out how to use  one low voltage switch to interrupt three  t stats  and three circulators.  How was that normally done.

  • Tim McElwain
    Tim McElwain Member Posts: 4,446
    Give me a list of what

    you have for equipment and controls and maybe we can sort this out.

    Normally if you have a low limit it maintains temperature in the boiler, in the case of a L6006 Honeywell or comparable SPDT from White Rodgers it would be wired (R to B) into the primary relay on your boiler which typically contains your hi-limit.

    When R to B breaks (due to set point temperature say 140° (F))then R to W makes and waits for a call from the thermostat. That will bring in the relay in the primary control and brings on the circulator for that zone.

    If there are added zones they would be wired through the primary control to insure high limit protection. 

    Are you getting domestic hot water from this boiler?
  • FredH
    FredH Member Posts: 18
    Inventory of existing controls

    Contact this user

    1964 American Standard Arcoliner  wideback with General fittings

    tankless (estimated  original cap 5GPM) 164,000BTU/hr Becket burner

    Hi Limit Detroit Lubricator (Breaks burner line voltage on temp) Set at 185 Deg (Coasts up to 200+ ) Closes at approx 160 Deg

    3 taco 007 circulators with 3 American Standard  circulator relays with terminals

    for TT and  SS terminals going to TT on  Honewell r8184 G controller on Beckett burner

    SPDT American Standard aquastat in tankless well is wired  NC(normaly closed) in parralel  back to TT on burner relay (however, it  is malfunctioning and not breaking on rise

    3 luxon programable thermostats (new to replace old Honewell mercury round)

    On  mid back back  of boiler is White Rogers 11d31-1 spdt wired to close on rise  (open on drop) to break

    line voltage to circulators on temp drop.

     Adjustable differential is set to as close

    to 0 as possible

    It was set set to 120Deg, I bumped it up to 140 deg but sometimes circulators will not turn on and boiler will hang a few degrees above 160 deg diff on hi lim switch on heat call. No burner or circulators. Probably due to cold water return after nightime setback.

    Put it back to where it was but boiler was still  just cycling between differential and Hi lim.

    Dicounected malfunctioning low lim switch and now burner and circulators run until call for heat is satisfied or till hilim and  then circulators continue.


    17 deg outside with all 3 circulators calling for heat, boiler  drops 

    to  approx 130 degs and  I still have hot water for shower.  Tankless does have

    30 gal aqua boost with its own circulator and separate aquastat. Not linked to burner

    Hence my original question. Since I can not use  the existing SPDT to break line voltage to circulator and also close 24 volt to turn on burner, i was just going to replace the controller in tankless well with a simple break on rise SPST with adjustable diferential.   Would act a low lim during off season. Circulators will remain independently controller by own aquastat.

    I think that is the way it was setup before tankless controller stopped working.
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