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Ideal boiler cycling? Opinions please.

MikeAmann Member Posts: 682
Now that I have my boiler running with decent combustion numbers, I am finally using it to heat the house. I was working in the basement last night and noticed that the boiler runs for about 3 minutes, 4 to 5 times an hour. Without getting too complicated with my entire setup, the heating side is wired to run it's circulator with a call-for-heat by the hallway thermostat. I did this on purpose. And that CFH is what is causing the boiler to fire, not the LO Limit of the aquastat. I added LEDs to my circulators and aquastat so that I could easily monitor what the system is doing. The hall thermostat is set to 65 F - Honeywell round and the anticipator is set correctly. I do have an Intellidyne HW+ Fuel Economizer (basically an indoor reset) connected to the aquastat, but I am hoping to keep that part out of this discussion. The only important part that applies concerning the HW+ is that it holds off the burner from firing if the water in the boiler has sufficient heat to satisfy the CFH. And it is doing exactly that, just like I want it to.

So the house is up to temp, the hall t-stat calls for heat, and the circulator runs. The boiler water temp is hovering in the 135-140 degree range. Maybe one minute later, the burner fires and runs for three minutes, then the CFH is satisfied and the burner turns off. Repeat 12-15 minutes later.

I think this situation is ideal, because I am not heating the water in the boiler up to the HI Limit and then hardly using that water for heating, giving me great standby losses.

What do you think about this? Thanks.


  • JakeCK
    JakeCK Member Posts: 1,128
    edited November 2021
    5 times an hour seems boarder line excessive. How cold is it where you're at? By comparison when its around 40f outside my very simple boiler will do a solid 15 minute or so burn and then shut down and it wont run again for another couple hours.
  • sunlight33
    sunlight33 Member Posts: 378
    Well, the ideal cycle is 1, boiler is constantly modulating its output so it matches the building heat loss.
  • JakeCK
    JakeCK Member Posts: 1,128
    Well, the ideal cycle is 1, boiler is constantly modulating its output so it matches the building heat loss.
    And after that the next best thing is to decouple the boilers output from the building so they can both be optimized. Such as using a buffer tank.
    EBEBRATT-Ed Member Posts: 13,126
    Your boiler temp is on the low end. It's operating like it's running on a low limit, I know it's not but thats what your controls are doing.

    In my opinion that is too many starts and stops for the burner. Burners always you get some incomplete combustion on every start and stop. 3 min of run time is not enough. Puts ware & tear on components

    Your run time is 12-15 min/hour. I would try and get the burner on time to at least 5min/cycle @3 times/hour would be better.

    I don't know what you have for controls.

    What I used to do at my house was the stat calls starts the burner and the circ and let her rip. If it hits high limit let it. When the stat satisfied the burner goes off. The pump stays on, I used to put a strap on aquastat on the boiler supply wired in parallel with whatever starts the circ pump so the pump is taking the residual heat out of the boiler and putting it upstairs.

    It will overshoot the stat a degree or so. Reverse acting strap on aqaustat makes on a temp rise set it to kill the pump when the water gets down to 130. nice and simple
  • MikeAmann
    MikeAmann Member Posts: 682
    edited November 2021
    Ed, so what you are saying is that you created a window for your circulator to operate within - between the HI limit and 130. I am doing the same using the HW+. I gave myself about a 60 degree window also, knowing that I would probably have to fine tune the settings. The short 3 minute run time was the reason for this question.

    I was able to split the aquastat's control of the circulators (don't ask how). The heating circulator is wired as a cold start (simple). The indirect water heater has it's own circulator and runs off the LO Limit of the aquastat, meaning that water no less than 140 can circulate through the coil of the IWH. The LO Limit must be reached before my controller gets power to run that circulator.
  • MikeAmann
    MikeAmann Member Posts: 682
    edited November 2021
    Ed, you understood the situation perfectly - It's operating like it's running on a low limit, I know it's not but thats what your controls are doing. I spent the entire night playing with the controls on the boiler trying to determine why I was getting that 3 minute run cycle 4 to 5 times per hour. To the best I can determine, it's either an overlap, or underlap, of the aquastat's LO Limit built-in 10 degree differential and the HLOLIMIT setting of the HW+ Fuel Economizer. I believe that what is supposed to be a 10 degree DIFF is actually somewhere around 20 degrees, maybe 25, and that is causing my problem.

    On a temp fall, the aquastat needs to release the burner to fire BEFORE the water temp reaches the HLOLIM setting of the HW+. But if the DIFF is screwed up by actually being lower, then it is the HW+ that is firing the burner. Funny, but with the house up to temp, when the hall t-stat calls for heat, all that is needed is a 3 minute circulator run to satisfy that CFH...... with 135 degree water!

    I love my HW+ Economizer, and it works very well. As I was sitting there watching all of this, I have a paper for a Burnham V8H boiler. What is of interest is the controller:

    Intelligent Oil Boiler Control

    Combines aquastat and relay functions into a single module.
    Two customizable integrated switching relays for easy addition of additional heating zone or indirect water heater.
    Energy saving “thermal purge”, which works by circulating residual warm water (140° or above) in the heating system before firing the boiler.

    Maybe it is time that I upgraded my controls. I now have the IWH added, so if there is a controller/aquastat that incorporates everything into one unit..............?

    But before I pull the trigger on that, if I can just replace the white block aquastat in my Honeywell R8182D for cheap, I would rather do that because everything is wired and working the way I want it to - except for that Lo Limit DIFF. Does anyone have a known good one for sale? Just the white block - triple acting.

    I don't have the time to do a rewire because all of my spare time is being taken up right now dealing with doctors, attorneys, probate court, memory care facility, financial institutions, social security, pension, etc. Dad has dementia and I am working on getting him placed in a facility for that. I am his conservator. I hardly have time to breathe.

    I can start another post for recommendations on a new controller. I will describe the must-haves for my system.
  • MikeAmann
    MikeAmann Member Posts: 682
    edited December 2021
    For those that want to continue following this: https://forum.heatinghelp.com/discussion/185686/help-me-to-select-a-new-er-boiler-control-aquastat-for-my-old-boiler#latest

    But the new, modern PLC based controls did solve this problem.