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Thermostats for Steam/Hot Water Hybrid

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Hello, 
We have mainly steam heating the whole house with a circulator pump taking the hot water from the steam boiler and circulating it into the radiators in the extension part of the house. 

Our unique situation comes with the two thermostats. Prior to Covid we had the old fashioned dial thermostats in both the living room and extension. They had to be changed as they were not serving our needs well at all and the heating was very unbalanced. 

Fast forward to 2020, I installed a smart Honeywell T9 thermostat for the living room with two sensors on the second and third floors. For the extension, I installed just a regular digital Honeywell thermostat. 

The thermostat in the living room, as far as I know, always controlled the boiler itself whereas the thermostat for the extension only controlled the circulator pump and had no effect on the burners igniting or staying lit.  

Here’s where the trouble starts. The boiler ignites only when the T9 thermostat calls for heat, as was always the case. However, now the boiler does not shut off until the extension thermostat is satisfied. The boiler will stay on and keep producing steam regardless of the indoor temperature (with the exception of the extension) 

The T9 is set to 70 and the extension is set to 72 as it’s above a crawl space and typically chillier than the rest of the house. The majority of the house will get as high as 78 sometimes even 80 and will keep going until the extension hits 72 and the problem isn’t necessarily consistent. 

If I manually shut the thermostat for the extension, the boiler and circulator pump will turn off. If I turn that thermostat back on to “heat”, the boiler will remain off until the T9 calls for heat but the circulator pump will run as intended. 

I can’t figure out if this is a new issue caused by my installing the new thermostats or if this problem always persisted but only now being noticed because the steam heated part of the house is balanced. 

Is there a scenario where if the extension calls for heat, the boiler can run at a lower setting and not produce steam?
If not, is there any idea how I can get the extension thermostat to solely control the circulator pump?

Thanking you in advanced! 
Mike 

Comments

  • Sylvain
    Sylvain Member Posts: 125
    edited February 28
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    the extension thermostat should
    - control the boiler water temperature via an aquastat up to the water temperature which was taken into account for the design of the extension circuit (180° ?);
    - control the extension circulator.

    Only when the T9 ask for heat, should the boiler be allowed to heat above the aquastat temperature to produce steam. The circulator should not run unless the extension thermostat asks for heat.

    You would need a relay commanded by the extension thermostat with two normally open contacts which would be closed whenever the ask for heat of the extension is NOT satisfied.
    In other words the relay is energised whenever the ask for heat of the extension is NOT satisfied, closing the contacts.
    - one in serie with the aquastat;
    - one to control the circulator (rated adequately).
    - The T9 would bypass the aquastat circuit (aquastat + relay contacts in serie with the aquastat)
    exqheat
  • Jamie Hall
    Jamie Hall Member Posts: 23,303
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    You are missing a control device, called an aquastat. This is a thermostat which is usually on the boiler in this type of installation which controls the boiler water temperature -- in most cases for heating only, it will be "cold start"; that is, it is a simple thermostat which is "on" when the boiler water temperature is below a certain value (which you set -- for heating, usually 180 F) and off above that. You can also get a triple acting aquastat, which -- basically, if it's wired up properly -- will control the boiler temperature between two set points, also has a high limit control which turns the boiler off if the temperature is too high, and has a low setting which only allows the circulator to run above a certain point.

    I think you just need the simple one.

    What the wiring is is simple. The thermostat for the steam heat controls the boiler as always -- just the two wires to T-T on the burner control. The thermostat for the hot water heat, however, is different: the thermostat is wired to a relay. That relay does two things. One set of contacts turns on the circulator. The other set is wired in series with the aquastat and in parallel with the thermostat for the steam heat.

    Now when the steam heat calls, the boiler fires and makes steam. When the hot water thermostat calls, the circulator turns on -- and, if the boiler water is cool, the boiler turns on. So long as this thermostat is calling, the circulator runs, but the boiler only fires if the water is cooler than the aquastat setting.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    exqheatMad Dog_2
  • mcs1925
    mcs1925 Member Posts: 9
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    Thank you both for explaining this in a way that’s so simple to understand. Upon further investigation, I see that I do have a Honeywell Aquastat. 

    Below is the mentioned Aquastat and the settings it was set to. 

     

    Below is the relay attached to the boiler. 

    The wires highlighted in Blue I am almost positive belong to the T9 thermostat. 

    The ones highlighted in Green I believe are for the extension thermostat 

    and the ones highlighted in Yellow I’ve traced back to the Aquastat. 


    Below is the picture of the full relay box and the diagram on the cover. 


    Is it possible this isn’t wired correctly causing the extension thermostat and Aquastat to not perform properly? 
    If it is correct, could it be that the Aquastat went bad?
    if there is a necessary component not pictured I’ll be more than happy to include it. 

    thank you again for your help! 
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
    edited February 29
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    There is a standard wiring system that will solve your issue. It is possible that the person that installed the addition system along with the RA832 and the Aquastat missed something and wired it incorrectly. There is also the possibility that the Aquastat is not installed in the correct location and is not stopping the burner when the boiler starts to make steam.

    The Aquastat should be installed below the water line in the boiler, not on a pipe that is external to the boiler. I will follow up with the proper wiring diagram shortly. It would be helpful if you posted a picture of the boiler so I can suggest a better location for the aquastat and also know what is operating the steam boiler.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    mcs1925
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
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    I selected a boiler wiring diagram at random. Your boiler wiring diagram can be substituted once I know what you have. the important part is where you connect the thermostat to on the boiler to make steam (as if you did not have any other zone).

    Then you will add a thermostat, aquastat, circulator relay and a circulator pump like i have illustrated here.


    I would suggest that you may need to move the aquastat to a different location, Or you may not need to based on how close the aquastat is to the boiler.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    exqheat
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,838
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    To follow up on the wiring diagram above, The thermostat for the steam (original) is connected directly to the boiler. That will get the burner to run long enough to make steam.

    The other thermostat operates the relay that will turn on the circulator pump. That relay also has low voltage contacts (X X) that will operate the burner. In order to keep the burner from making steam when the water zone is the only zone calling for heat, the Aquastat should be set at 160° or 170° so the burner will stop operating before it makes steam. That aquastat needs to be in the hottest portion of the hot water zone or inside the boiler below the water line. That way the burner will stop before it gets to making steam.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
    exqheat
  • exqheat
    exqheat Member Posts: 185
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    Locate strap on Aquastat as close to the pipe exit from the boiler. Conduction will keep it closer to actual boiler temps. Wire extension thermostat in series with this aquastat to the TT for the steam boiler. Set aquastat to max 160. You can adjust to suit asa the season changes.
    John Cockerill Exquisite Heat www.exqheat.com Precisions boiler control from indoor reset.
  • Sylvain
    Sylvain Member Posts: 125
    edited February 29
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    exqheat said:

    Locate strap on Aquastat as close to the pipe exit from the boiler. Conduction will keep it closer to actual boiler temps. Wire extension thermostat in series with this aquastat to the TT for the steam boiler. Set aquastat to max 160. You can adjust to suit asa the season changes.

    the relay is needed
    The circulator should work when the extension-thermostat asks for heat even if the burner is shut down because boiler water temperature is high enough (between aquastat temp and boiling temp).

    Furthermore, placing the aquastat on a pipe will not measure boiler water temperature if there is no flow in that pipe.

    Anyway the op has the relay (apparently not correctly wired) already installed.
  • mcs1925
    mcs1925 Member Posts: 9
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    Good evening all,

    I followed the wiring diagram Ed shared and compared it with the existing wiring setup. 

    I assumed the thermostat wiring was correct and traced the two wires screwed into the (X) terminals and saw that they were reversed compared to what the diagram shows. So I switched them, turned the T9 thermostat off and only left the extension on. 

    No immediate difference however I figured I’d turn the dial on the Aquastat just to see if anything would happen and to my surprise,  when I turned the dial down to about 65, the boiler ignited! 

    I let it run for a while and turned the dial to about 145 and let it cycle on and off as it needed to monitor the temperatures throughout the house. Almost every sensor with the exception of 1 (the third floor dormer which is always much cooler) read 72. This was the most evenly distributed heat I’ve seen. 

    I am curious as to why I had to initially dial it down to 65 in order for the boiler to ignite. Shouldn’t it have ignited once the water dipped below the original set temperature of 180? 

    Anyways, I definitely plan on moving the Aquastat for a more accurate reading going forward. 

    As requested, here are pictures of my boiler for further observation. 

    It’s a Peerless boiler installed in 2000




    Better angles of both sides 



    Below, I’ve circled the Aquastat which is attached to the return line for the radiators in the extension. 

    The pipe I outlined in red is the supply line.
      



  • Sylvain
    Sylvain Member Posts: 125
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    "I am curious as to why I had to initially dial it down to 65 in order for the boiler to ignite. Shouldn’t it have ignited once the water dipped below the original set temperature of 180? "

    Some corrosion or gummed lubricant which was impeding the aquasteat mechanism because it hadn't worked for some time?
    I don't know if it is advisable to put a little drop of oil here and there on an electric appliance. Although it is only 24V.
    Anyone knows about a dielectric lubricant ?
  • mcs1925
    mcs1925 Member Posts: 9
    edited March 3
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    I moved the Aquastat to the supply pipe close to the boiler. 
    It seems like the Aquastat generally doesn’t sense the temperature accurately. 

    When I turn the dial on the Aquastat to a lower number say close to 60, the burners ignite but when I raise anything past 100 it the burners shut off. 

    It seems to think the water is already above lets assume around 100 degrees; but the supply pipe is cool to the touch. 


  • Sylvain
    Sylvain Member Posts: 125
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  • mcs1925
    mcs1925 Member Posts: 9
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    Hey Sylvain 
    am I supposed to be able to see something labeled with a B R or W? 
    I’m having trouble identifying what that is or where to locate it. 

    Not sure if this matters but I see the diagram shows an example for an oil fired boiler. I have natural gas. Not sure if that makes a difference. 

    Thanks! 
  • Jamie Hall
    Jamie Hall Member Posts: 23,303
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    oil or gas makes no difference. Remember, the thermostat is just a switch, nothing else.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Sylvain
    Sylvain Member Posts: 125
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    mcs1925 said:

    Hey Sylvain 
    am I supposed to be able to see something labeled with a B R or W? 

    I’m having trouble identifying what that is or where to locate it. 

    Thanks! 
    It is in the aquastat.
    look at your second picture in your comment here:
    https://forum.heatinghelp.com/discussion/comment/1793588/#Comment_1793588

    B is the currently unused middle contact;
    W is where your white wire currently is;
    R is where your red wire currently is.
    Don't move the R wire.
  • mcs1925
    mcs1925 Member Posts: 9
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    Amazing! That did the trick! 

    I’ll let it run for the time being to see how everything works out and if any issues arise. 

    But if nothing, I can’t thank you all enough! Thank you all for your time and assistance with this. 
  • Sylvain
    Sylvain Member Posts: 125
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    For your documentation, the shematic of the RA832 is here:
    https://customer.resideo.com/resources/Techlit/TechLitDocuments/60-0000s/60-2481.pdf

    see: Fig. 3. Internal schematic and typical hookup for RA832A
    mcs1925
  • mcs1925
    mcs1925 Member Posts: 9
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    Much appreciated. Thank you for this!