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Honeywell aquastat DUU setting

<span style="color:#000000">I

recently had a Honeywell L7224 aqua-stat installed. I also have an

indirect water heater installed and Argo ARM 3P Switching Relays With

Priority. My issue is that I am running out of hot water. I have my high

limit set to 190 and my low set to 170 with a differential of 10. My

boiler will not fire up until it goes below the low limit. I would of

expect the boiler to fire up as soon as I it notices that the hot water

heater is in use. I have the arm3p set with priority and wired to the zr

and zc terminals of the aquastat. I was unsure as with on of the

setting. Should the DUU setting be set to on or off. Also, with the

arm3p controller should the boiler turn on when immediately when it is

being called for hot water or should it wait until it hits the low temp


thanks in advance



  • RobbieDo
    RobbieDo Member Posts: 131
    Do you

    Do you have it setup for priority? Do you have the DHWH on a zone valve or a pump?
  • Dewey
    Dewey Member Posts: 10
    I have

    I have it set on priority using a Grundfos UPS 15-58 3 speed pump.  I have the pump set to low as the Superstor 45 recommends 8 gpm flow rate. 

  • Big Ed_4
    Big Ed_4 Member Posts: 2,065
    Enough Hot Water

    When running out of hot water , we would look at the size of the storage , flow rate of shower heads or size of the tub and length of usage ... We all like a high volume shower but one would empty a tank rather quickie ... Lets say you took out the water restrictor , it could increase the flow rate to 5 gallons per min . With a 45 gallon tank the head would you a 8 min shower ... A two gallon per min would give you a 22 min shower ... Recovery is important to build up the tank for the next shower... We would look at that if your problem is the tank is taking too long to build up ...

    To check your flow rate is how much water you can collect in a five gallon bucket with in a min...
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10
    Will try it

    Thanks I will try the 5  gallon bucket.

    How do I determine what the recovery rate is of how water tank.  Also do you know what the DUU setting should be set to on the Honeywell L7224 aquastat.

  • Big Ed_4
    Big Ed_4 Member Posts: 2,065
    DUU settings

    The DUU setting should be off unless you also have the outdoor reset and hot water module ... Which is a nice addition ..

    The recovery depends on flow rate , Water temperature ,boiler supply piping and boiler output ... But assuming the norm , a good rule of thumb is one gallon per min 50K output ....
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10
    Still not getting hot water

    I did not bother dong the 5 gallon bucket thing, instead I read the instructions on the shower head and it is rate for 1.5 gpm, so that will give me about 15 minutes per shower with a 45 gallon tank. 

    I am still confused about he set with the indirect hot water tank, especially the duu set on the aqua stat.  You had mentioned that it should be set to off unless I have the outdoor sensor or a hot water module.  I have neither on the Aqua stat but I do have an Argo 3p relay with priority.  When I ran the hot water and it reached the low limit with the DUU setting on off, the circulator did not shut off and the temp of the boiler continued to drop to about 145 before it started to recover.  I turn the DUU setting on and the once it reached the low limit the ZC led light came on, on the aquastat and the circulater turned off and the furnace was started to recover from the low limit of 170 ( give or take a few degrees based on the differential)  So I think I have that solved that the DUU setting should be turned on in my situation.  But I am still confused about this setting.  I and whether I have it correct.  When calling for heat the boiler kicks in right away if it is under the High limit, but when calling for hot water the boiler only kicks in when it reaches the low limit.  Should the boiler not kick in at the same point whether it is calling for or hot water.  So I decided to read over the manual porbably for the 10th time and read this

    Table 6. L7224 Controller Operating Sequence with

    Domestic Hot Water connected trough the ZR


    Action System Response

    Zone Request (ZR)

    terminal is connected to

    L1 (Domestic Hot Water

    calls for heat).

    Boiler temperature is checked.

    Burner starts when water

    temperature is below High

    Limit setting.

    So now I am thinking, does the ZR hook to the L1 from the argo controller?  As it states the "the boiler starts when the water temp is below the high limit. "

    I am now totally confused.

    Here is the link to the manual


    thanks to everyone in advance
  • Big Ed_4
    Big Ed_4 Member Posts: 2,065

    Is terminal C1 in the Honeywell being used for the Indirect or a heating zone ??? What type and brand name boiler is being used ? ZC and ZR terminals are used to expand additional zones under the dual aquastat in the Honeywell ... The aquastat will maintain minimal boiler temperature through the low limit .What setting depends on boiler and system ... The low limit would prevent C1 and ZC to be powered until Low is satisfied or reached low limit ..The boiler will maintain low limit unless terminals TT are made or if power is sent to ZR ... Then boiler temperature will reach high limit setting ...

    A 1.5 gal min head; 45gal / 1.5 gal min would give you 30 min shower ... A 2.5 gal min head ; 45 gal / 2.5 gal min would give you a 18 min shower ... A rated 2.5 gal min head with the resister pulled would give you around a 10 min shower
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10
    Info Requested

    First of all let me start by saying thanks I really appreciate the time you are taking to answer my questions.

    My Boiler is a Detson Model HMT  http://www.dettson.ca/Docs/Manuels/X40019.pdf

    Here is how the technician wired it up:

    Aquastat   ZR to the ZR on the Argo Relay

    Aquastat   ZC to the ZC on the Argo Relay

    L1 - Black wire - Goes to the line relay (Main power box)

    L2 - White Wire - Goes to the line relay (Main power box)

    C2 - is empty (no wires attached)

    B2 - White wire - goes to the boiler

    C1 -  is empty (no wires attached)

    B1 - Black Wire - goes to the boiler

    On the Argo controller

    Zone one Priority goes the Circulator for the Hot water

    Zone two goes to the circulator for the heat.

    I have attached word document with some photo
  • Big Ed_4
    Big Ed_4 Member Posts: 2,065
    Looks Alright

    You have a steel boiler with a blank coil plate so you want to maintain minimal temperature to prevent condensation , combustion condensing and leakage . I would have wired it to ZC/ ZR as well to protect the boiler ... I would set the low at 120 * with a 20* diff ... The High , cast iron radiation 160* 10* diff , fin and tube 180* 20* diff .. The boiler should maintain between 110*-130* if I figured my diff drop correctly ... When either the hot water or single zone heat calls the burner will fire up to high limit , 10 over on the 180* setting , drop 10* below and fire up again ... Circulators will turn on with temp rise on the low ... This will keep the boiler water hot enough to prevent combustion condensation .

    The DUU setting Is used when an outdoor sensor and hot water module is used straight from Honeywell...

    You Welcome :)
    I have enough experience to know , that I dont know it all
  • Ron Jr._3
    Ron Jr._3 Member Posts: 603
    edited February 2011
    Honeywell instructions for this aquastat

    are very lacking . I'm reading my copy and all it talks about is using the ZR terminal for an indirect only . I'd try what you attempted before - set the DUU to ON . Like Ed said , I'd set the low limit much lower ...  If the system is working properly the boiler will maintain that low setting till a call for heat or hot water bumps it up to the high setting .

    If all else fails , I'd disconnect the wires from ZR / ZC and connect the isolated end switch of the Argo to T-T of the aquastat .
  • Dewey
    Dewey Member Posts: 10
    setting questions

    Hi all,

    Thanks, I am still a little confused.  When the indirect calls for hot water the boiler will only kick in once it is below the low limit.  So to set the low limit to 120 as opposed to 170 where it is now,  will that not take much longer to for the boiler to come up to temp.  So correct me it I am wrong.  The boiler temp is at 120.  The hot water heater calls for hot water and then the circulator kicks in and the boiler starts sending hot water to the indirect heating the cold water.  At this point the temp of the boil will start to drop, once it gets below the low limit the circulator will shut off (because we have the duu set to on) and the boiler will continue to run until it hits that high limit. At some point and time the circulator will turn back on and start  heating the cold water in the hot water tank, but by the time this all happens, I have run out of hot water

    Also what is advantage of hooking the isolated end switch to the T - T terminals.

    Thank again, I do apologize for all the questions I am trying to wrap my head around this.  Thought this would be and easy decision and install to save me some money on oil, but it is seems to be getting complicated as time goes on.  Thanks again.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,065

    ..Check the wires between ZC and ZR between The Argo and the Honeywell , Are they color coded between them , double check if there is a box in between .. I can not see on the Argo in picture ...Hmmm wonder if they are crossed...
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10

    The appear to be Ok the the ZR goes to the zr and the zc goes to the zc.  There is no box between them.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,065
    edited February 2011
    Something is wrong

    If the heat zone calls does it does the same thing ? Just bounce off the low ?

    Noticed you mentioned before , when the heat call the temperature bounces off the Hi.... But not the indirect in the same relay ???? You need someone with a meter to see if ZR terminal on the Argo charges up when the indirect calls ? You may have a bad ice cube relay or board .... In the mean time or a way around the problem as Ron mentioned if you run a 18-2 or better wire between terminals XX Argo and TT Honeywell , it will run up to Hi limit as well... Another way to wire up the system... Just using another option
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10
    honeywell l4080

    Hi all,

    I has been a while.  I am still having issues with not enough hot water. One thing I thought about was raising the temp of my water heater.  At present it is at 130, I thought I would raise to 140 to see if that helps.  When I remove the cover to the Honeywell l4080 temp sensor in the hot water tank, I noticed a diagram/chart on the cover. It stated that if there is 1.5" of insulation the insertion depth should 11/4 inches with 3 inches of insulation it should be made longer.  My superstor ssu45 has 2 inches of insulation.  would the sensor not being long enough cause the boiler to kick in late and not heat up?  I noticed that I have to run the hot water a long time before the boiler kicks in and starts reheating the water.  Should I take the sensor out and extend it?

    thanks as always

  • Big Ed_4
    Big Ed_4 Member Posts: 2,065

    Make sure the sensor is fully inserted in the well ...
    I have enough experience to know , that I dont know it all
  • Dewey
    Dewey Member Posts: 10

    Thanks Big Ed. Since I have never done this before.  I assume I have to shut off the power, the water to the tank and drain the tank before  I can remove the sensor?

  • Big Ed_4
    Big Ed_4 Member Posts: 2,065
    Sensor or Capulary tube

    Not sure what control is used for the hot water tank but make sure the probe is fully inserted into the well .. The well will isolate the the capillary tube or sensor from the water in the tank ..
    I have enough experience to know , that I dont know it all
  • Eric_32
    Eric_32 Member Posts: 267
    edited March 2011
    Ya know....

    It's possible that the well in that indirect has some build up on it and the heat isn't passing thru to the sensor inside it.

    Maybe draining down the tank, remove the well and clean inside and out and reinstall. Might make a difference.

    How old is the indirect?
This discussion has been closed.