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Aquastat settings for wood boiler & indoor oil burner

I read alot of aquastat posts. I'm still missing something. Please help.

Ok. Keeping this short as possible.
I hooked up an outdoor wood boiler to automatically work with my indoor oil fired hot water baseboard boiler. There are 4 zones.

The honeywell triple aquastat is what's giving me a hard time. I wanted it to turn on at 140f and turn off at 185f. If the wood boiler and plate to plate heat exchanger dropped to 140 wanted oil burner to turn on and heat the boiler to 185.
I set the low to 150f. And the diff to 20f. Thinking it would come on 130f and keep going until 185f. The hi limit setting. Doesn't seem to be the case. Seems like low setting does all the controlling and high is just a safety?


  • Jeff02892954
    Jeff02892954 Member Posts: 5
    Thanks in advance. I know the post is jumbled together:: sorry.
    P.s there is another basic aquastat that turns off the wood boiler circulator if the supply temp drops below 140F. So it's not heating the water all the way out to the wood boiler when oil boiler is running.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited November 2017
    So what is your actual sequence of operations? What temperature does the boiler get to? If it's not reaching high limit, that can be a good thing, meaning you are designed for proper thermal equilibrium, BUT, if it's not gaining temperature, then that would mean you're not putting enough BTU's into the system.

    The high limit should be more of a safety setting then an operating setting but that doesn't happen as often as it should.

    May be best to post a schematic, can be hand drawn, of the piping and all the components, with an explanation of how it is wired.
    Keep in mind, if you're temperature sensor isn't making good contact with your well, or the well is scaled up on the boiler side, those dials aren't going to be accurate representation of the boiler water temperature. As a matter of fact, as time goes by, they're usually not that accurate. Assuming your gauge is accurate, a simple test would be to slowly turn the dial to see where the circulator (clicks) kicks on/off, and note the temperature. The same for the high limit, note where the burner kicks off/back on. I've seen the high limit on 140° and the burner kicks off/on at 200°

    Here's a generic triple aquastat manual. Note Page 5, figure & for sequence of operations/differentials, etc.

    There was an error rendering this rich post.

  • Jeff02892954
    Jeff02892954 Member Posts: 5
    Thanks for taking the time to write me back. The wood boiler does seem to be operating correctly. Though today I let if run out of wood to test the back up settings. When I set the Aqua stat low to fire oil burner at 140F it seems to fire 130f and then stop at 140f. I really like it to stay on oil until it hits 185F. If only the diff setting alows it 25 degrees. So the max I can get it 165f and it shuts off.
    One thing that worries me reading the manual is how the zone controller works. I don't want it to lock out circulators until it gets to temp. I don't think that's happening though.

    I included a photo and hand sketch. All seems to be working except the backup settings. This am the outdoor unit was out of wood. The home was dropping in temp. The indoor boiler was firing though it was turning off at 140f or 150f there for the home was still dropping temp it was about 22F outside.

    I will read through that manual again. I just hoped those aquastat would turn on at the low and off at the high. But that would be to easy though. Lol. Thanks again.
  • Jeff02892954
    Jeff02892954 Member Posts: 5
    Sequence of ops winter condition:
    1. wood boiler running, thermostatically internally controlled 180F average. Water temp

    2. Water circulates through plate to plate heat exchanger heating indoor boiler to 174*F approx.

    3. If the wood boiler fails, a simple stand alone aquastat will stop the wood boiler circulator pump to stop pumping and reverse heating all the water in wood boiler once oil burner fires.

    4. The oil burner fires up once it senses the internal core temp dropped below 140F. And runs until it gets to 180F and shuts off.

    5. The boiler runs off oil to 140-150f and shuts off again. Need this to stay running until it hits 180f. To be able keep up with thermostat set temps.

    6. Wood replenished in boiler. Temp increases to set point and turns wood boiler circulator pump back on . Wood boiler begins heating boiler core temp there for not running oil.

    * I will check the actual temp with my meter or non contact. That's really the only issue. If I set the Aqua stat to 140F it only runs to maybe 150 and shuts off. I have the high set to 180f. That's where ideally it will shut back off.
  • leonz
    leonz Member Posts: 1,159
    edited November 2017
    Speaking as an owner of a wood and coal boiler and an oil boiler that were tied in parallel for 34 years I think know what is wrong with your forest eater and oil burner set up.

    Can you provide us with an image of the forest eater controls and wiring connections on the back of the forest eater?

    You need an electrician for three hours work or so and some parts.

    YOU NEED AND SHOULD ONLY HAVE ONE TRIPLE AQUASTAT TO CONTROL BOTH BOILERS and the circulators ON THE OIL BOILER STEAM CHEST ONLY in concert with your circulator on the forest eater that is operating pushing water in the loop through boilers rather than using a heat exchanger as much of your problem is there since the water is not being pushed into the oil boiler sump and returned to the forest eater.

    YES it does work and it worked that way for me for 34 years on my hand fed wood and coal boiler.

    I had also had two strap on aquastats and a cube relay control on the wall for the dump zone which is my existing heating loop

    YES it can be done and done right this way.

    The oil boiler will only come on when the forest eaters fire has diminished or gone out as long as the wiring and plumbing is done right.

    If I have this correct both your triple aquastats are arguing with each other due to the plate heat exchanger being used rather than the water coming and going from the oil boilers sump to your forest eater.

  • Jeff02892954
    Jeff02892954 Member Posts: 5
    Thanks Leonz! I'll work on some photos of the wood boiler. There's not much to the controls. Just turns on/ off at 160 on 180 off. The circulator is wired off the single aquastat to just open under 130f. I used a plate exchanger due to reading that the boiler is under pressure and wood boiler is open to atmosphere. I'm intrested in how you set yours up though. Rite now I put the triple aquastat on the oil burner to low 150F high 185F and 25F diff. It seems to work alright now when it runs out of wood. But I would like to still increase off temp to 180F or better without increasing the low or on temp.

    Ps. I am a licensed electrician. Any diagram you have on your relay setup I'd greatly appreciated. I though about grabbing a contact off the triple aquastat. I was trying to be at least invasive as possible on existing boiler.

    Side note. Your not kidding "forest eater" I was in Florida and now in PA I split 3 cords of wood thinking it would be plenty. At this rate probaly going to use 10 cords.
  • leonz
    leonz Member Posts: 1,159
    I had my high limit at 160 and low limit at 140 with the wood boiler and the oil boiler both with the triple aquastat in the steam chest of the Buderus Logana G205 oil boiler

    The honeywell relay cube box was connected to the house circulator to activate the dump zone and also operate the circulator in normal heating with one of the strap on aquastats from what I remember. I no longer have the old boiler or wiring etc.

    I will tell you a little secret that you cannot tell anyone;
    I filled my firebox half full of full firebrick to the flue breech.
    which allowed me to also burn anthracite nut and stove coal very well too.

    I laid a 2 by 12 inch by 12 inch piece of channel iron on the shaker grate frame and then stacked the firebrick all the way to the flue breech and I saved a huge amount of wood and coal as the fire burned more efficiently and I had much less smoke too.

    I had the dump zone temperature set at 190 from what I remember and a 10 degree differential I think and that was set for both boilers

    I used more than 15 cords of softwood in some years when I was able to get hemlock slabwood.