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rjkrjk Member Posts: 5
I have a l7224 honeywell electronic aquastat  controlling a oil furnace. There is one circulator for 2 zones, 1st zone for heating and second zone for heating a indirect hot water tank for domestic hot water.Each zone has its own hydronic zone valve. 1st zone valve is controlled by a wall thermostat on the main floor. The 2nd zone valve is controlled by the thermostat in the indirect boiler,the contacts on the zone valves are paralled and go to terminals  tt on the aquastat.The burner is on B1 B2 of the aquastat and the circulator pump is on C1 C2.When either zone calls for heat the burner starts and brings the water up to the high limit set at 170. The burner then shuts down and restarts at 160 because the high diff is set at 10. The problem I'm having is that the c1 c2 terminals never put out 120vac to start the circulator. However the cast iron rads get hot because of convection and eventually warms the house. This is the way it was when I moved in and just noticed that the circulator never runs on a call for heat from either zone. I read the manual and I am confused on the low limit setting for this system I want a cold start system so what should the low limit setting be on in order to get the circulator to start on a call for heat or DHW.If the low limit is turned off  will the c1 c2 terminals ever start the circulator.


  • icesailoricesailor Member Posts: 7,265
    Electronic Aquastat:

    That control will do many things that the controls it replaced could only do by themselves. There is a way to set it up to do what you want. If the instructions are there, you may be able to figure it out. But they are not easy to understand. I doubt you know enough to muddle through the process.

    That said, in my personal opinion, it is a really good idea to set that oil boiler up as a cold start. It will condense like crazy and form a box or two of Kibbles and Bits inside the passageways. This debris must be cleaned out thoroughly every year and most cleaners only do a barely acceptable job. It can take me over two hours to clean a boiler like yours. My own personal oil boiler (W-M WTGO-3) is a warm start. I have the operating/low limit set at 140 degrees and the high limit at 170 degrees. Every year, I clean the sections/passageways with a fluffy radiator brush and the brown ash residue just falls into the chamber and gets burned off.

    You are probably victim of the installer or someone previous to you who doesn't read well and didn't read the operating instructions for the control.

    Unless you can figure out the sequencing of the buttons in the control, you may need professional help.

    OBTW, dirty, plugged up boiler passageways do not promote fuel savings.
  • Paul48Paul48 Member Posts: 4,492
    edited January 2012

    have verified no voltage at c1 and c2 with a meter? If you set it up as cold start, you are shutting the low limit off, and on a call for heat the burner and circulator should turn on at the same time.
  • rjkrjk Member Posts: 5
    Verified no voltage

    Yes I have verified this with the meter. No power on c1 c2  when boiler is running. I never went into settings yet maybe low limit is on and set above high will this cause the circulator not to start . What should the settings be
  • Paul48Paul48 Member Posts: 4,492
    edited January 2012
    Turn it off for now to check the pump

    Set it for cold start, or  Press the "I" button until LL shows what the low limit is set for. In run mode, each press of that button will show a different parameter.
  • rjkrjk Member Posts: 5
    Explain how LLsetting works

    Manual is hard to understand when it comes to LL settings. Can you give me a explanation of the different scenarios for the low level setting.If I set the low level to on what will take place when the thermostat calls for heat or the indirect tank calls for heat.

    All I want is the circulator to come on when thermostat calls for heat to start moving water. Thanks for your help its becoming clearer.
  • Paul48Paul48 Member Posts: 4,492
    Low Limit

    The Low Limit is simply the temperature the boiler will maintain itself at, awaiting a call for heat.It provides a "head-start" for the boiler(if you will). Now on a call for heat, or hot water, the low limit is by-passed for the application of the burner. In other words, it turns on and will only shut off when it reaches the high limit, or the demand for heat is satisfied. During a call for heat, the low limit does control the circulator, turning it on or off to keep the water circulating at the desired temperature. Make sense?
  • rjkrjk Member Posts: 5
    Low limit

    Thanks Paul48

    Tell me if this is right. I set the low limit to off.  Then set the low limit setting to 140 degrees. I also set the High limit to 160 and the high limit diff to 10. If no thermostat calls for heat nothing will ever happen. If a thermostat calls for heat the burner starts and the water temp in the boiler rises. Once the water temp hits the low limit setting of  140 degrees the circulator will start.The burner and circulator continue to run together until the boiler water temp hits the high limit setting of 160 degrees.At this time the boiler shuts down on high limit but the circulator continues to run as long as the thermostat is calling for heat. When the boiler temp falls to the high diff setting of 10 degrees below 160 degrees the burner starts again till it hits 160 degrees and shuts off. This cycle will continue until the thermostat is satisfied and shuts everything off again.If for some reason during this cycle the water temp in the boiler falls below the low setting of 140 degrees and the thermostat is still not satisfied the circulator will shut off but the burner continues to run until the water temp goes back above 140 degrees and the circulator starts again.Once the thermostat is satisfied everything shuts down and will not start again until the thermostat calls for heat.

    Now if I set the Low limit to on  and set the low limit to 140 degrees with  the low limit differential set at 10 regardless of the thermostat calling for heat the burner will start to maintain the boiler at 140 degrees for a domestic hot water coil.

    Am I right in saying this?
  • Paul48Paul48 Member Posts: 4,492
    cold start

    If you set it up as cold start (turn low limit off). On a call for heat or hot water, the burner and circulator will come on and run until either demand is satisfied. There is no longer a low limit setting.
  • rjkrjk Member Posts: 5
    Got It

    Thanks very much Paul48 for your help understand how it works now. You are much better explaining it than the manual.
  • lisaDlisaD Member Posts: 1
    low limit OFF boiler still coming on

    Paul.  I have a pellet stove for heating our home and still have the hot water tank (amtrol) connected to the boiler for our hot water  We have set the aquastat to OFF at the LL, to create a cold start; however, the boiler is still coming on during the day even when the hot water is not being used.  It seems to still be coming on below about 140F.  Any idea?

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