oil heat forced hot water ???

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by surfbug, Jan 14, 2007.

  1. surfbug

    surfbug New Member

    Jan 12, 2007

    My thermostat controls the circ pump.

    but not the "fire" in the furnace.

    I have the lower control limit at 120

    and the upper at 140

    house is empty just want pipes not to freeze....


  2. surfbug

    surfbug New Member

    Jan 12, 2007

    here is more info....

    house is in allentown pa, and is a rental

    5 br with full basement and three floors, row home.

    the system has one burner in the basement, 275 gallon tank in the basement hallway.

    the system has three loops, one for each floor. these are controlled by mini butterfly's, never seen these, they act like a butterfly valve, but have little 3/4 tabs to control flow, instead of a big 4 inch handle types....still butterfly valves and same principle, right?

    system has one thermosat, a programmable one, cant remember the name
    just bought last year, has touch screen, pain in the ass......7 day 4 time periods per day....

    system is at least 25 years old, emf or emi burner.

    new items in last 3 years

    circ pump
    honeywell controller/red button thingy
    new electrodes
    recent cleaning and tune up...(1/2 professional, not measurement of temps...stack temp stuff like that...what should be measured anyway and how?)
    new shut off at burner....this is the second one, there is also an emergency shutoff at top of steps
    new drain valve, press relief valve
    system has expansion tank

    when the thermostat is set at 45, (remember, just want to keep circulation to prevent heater pipes freezing....I am gonna shut off the water to the home....).....

    HERE IS THE problem....

    therm at 45 deg

    room temp says 58 on therm

    I would expect the burner to be shut off, along with the circ pump, until the temp trips below 45...

    then the burner should turn on, heat till the upper limit of 140, (set down from 180, just to save fuel....no one in house, jsut want to keep heater pipes form freezing..)

    then the circ pump should flow this hot water thru the system, and heat the therm back to above 45, .....then shut off.....circ and burner....

    I want it to work this way, because, it has been warm during the day....45-50 degrees, but some nights it goes down to 27-30....

    now, this week it is going to 17 degrees.....I am sure I will use the burner more then....

    I want to conserve fuel, and only have the BURNER come on when the HOUSE THERM goes below 45 and triggers to circ.....

    but it seem that when I turn on the burner, even if the set temp of 45 on the therm, and the room temp is higher, the burner still......

    fires to get up to the upper control limit.....

    pump wont circ, that is ok, room is warm.....

    but why is furnace firing and warming to upper control limit, when room is warm enough>?

    get it?

    shouldn't both the circ and the furnace fire operate off the THERM?


    BTW, I am new here, :eek: sorry for the long confusing post, but hey, gotta start somewhere....

    al :p
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  4. rmelo99

    rmelo99 Network Engineer

    Jul 7, 2006
    Network Engineer
    The aquastat on the boiler operates off of it's upper and lower limit temperatures, usually independent of the thermostat.

    The thermostat triggers the circulator when the room is below temp. B/c the circulators circulates water through the houses radiation the water loses temperature when it returns back to the boiler, therby lowering the boilers temperature. When that temperature of water coming into the boiler gets to a point below the aquastat's limit it will fire the burner.

    I'm not a pro at this just my knowledge of how the boiler controls typically work.

    If the circulator isn't running then I would guess that the thermostat is working since it isn't turning it on. I would guess that the aquastat on the boiler is just keeping the boiler at temp. The upper and lower limits might not be exact on the aquastat based on age and installation of the temp sensing bulb in the boiler. If you check out the guage on the boiler it should have a temp reading. See what the reading looks like when the burner is firing. My guess is that the temp has simply dropped on the boiler's water and it is firing for just a short bit.
  5. surfbug

    surfbug New Member

    Jan 12, 2007

    yah, it does make sense now, that you say it, that the aquastat functions seperate of the thermostat.....

    BTW, if I want heat, everything works fine.....the system is ok...

    I am trying to find a way to keep the system JUST above freezing, so that the pipes dont freeze as the temps drop.

    I know I have been burning less fuel now that I dropped the lower and upper control limits....they are now 120 and 145.....

    Question: on the aquastat, it says to keep the upper and lower control limits at least 20 degrees apart....why?

    So, maybe I should put the lower control limit at the lowest I think it is (100 degrees)....and put the upper limit at 130 or 120.....very low.....

    to attain my goal of having the heating system just hot enough so that the pipes dont freeze....

    maybe I am being to critical about it....

    but ultimately I would like the THERMostat set at 45 degrees, and have the circ pump and burner fire at the same time....

    I have a temp guage on the system, and it does seem to follow the aquastat settings....

    Question: some aquastats only have a high limit, and no lower control limit.....
    why is this? is the lower not needed, cuz it was just uses the ambient temp of the room/furnace?

    thanks for answering these basic questions!


  6. surfbug

    surfbug New Member

    Jan 12, 2007
    I am gonna get a timer and hook it to the furnace power.....

    kinda like a 120 volt light timer...(the kind to run the a light in the house on or off, to make it seem like someone is home when they are on vacation)...so it turns off the furnace during the day, and turn on power to the furnace at night, then the aquasat and the thermostat will function normally .....

    any other info to some of the other basic questions in my post would help....

    but I know that the aquastat and the thermostat function independantly......

    that was a big piece of inof, and helps me figur out what is up....


  7. jch

    jch Member

    Jan 3, 2006
    Victoria, British Columbia, Canada
    Don't set your boiler temperature too low or else you'll rot it out in no time from condensation.

    Oil burners produce a lot of water vapor.

    The metal boiler surface has to be warm enough to prevent this vapor from condensing on it. Condensation on outside of boiler, combined with acidic soot (SO4) means sulfuric acid all over the outside of your boiler core. You'd be lucky to get a year out of it. Therefore, Minimum 140F.

    Typically you'd set it at 180/140 (high/low limits) for big cast iron rads or 195/160 if you're using convector rads (the ones with the million fins in them).

    You want at least a 20 degree spread in the settings so that the burner is not constantly cycling on/off. Cycling creates a lot of soot and water vapor.

    Does this help?
  8. surfbug

    surfbug New Member

    Jan 12, 2007
    yes....that does help

    I have big rads....I think

    they are the pipes where the soot collects, right?

    I think it was set at 140-180 but I lowered it to conserve while the house is empty.....

    I can raise it back, in fact what I will do is raise the hi limit to 180 while I work on the place during the weekends....

    then turn it back down for the week when I am not there, until I get a tenant in there....

    you said 180-140 minimum 20 degree spread....but this is 40 degrees///....

    I understand why the lower would be 140.....but why so high on the upper?

    to conserve, could I do 160-140?

  9. jch

    jch Member

    Jan 3, 2006
    Victoria, British Columbia, Canada
    I'm talking about the radiators throughout your house. Are they big cast iron ones? Or do they have a bunch of thin aluminum fins on them?

    No, I'm not talking about the boiler itself.

    Yes, 20 degrees *minimum* spread.

    You could do whatever you want. But for heating efficiency, the higher the boiler temperature, the higher the heat transfer into your living space. But you'll also have higher standby heat loss.

    Basically, your burner will turn on and off to keep the *boiler* temperature between the two settings you choose.
    - Too cool on the lower number and you'll destroy your boiler through corrosion.
    - Too high on the higher number and your boiler could over pressurize and explode if your pressure relief valve fails.
    - Too high on the higher number and people touching your rads will get burned.
    - Too high on the higher number and you'll have bigger heat loss when the furnace is in standby (keeping that water so much hotter than the surrounding air in the basement).

    The >20 degree spread is to make sure that the return water is still hot enough when the pump is going so that the burner won't turn off.

    Every system is optimized for a desired heat drop between source water temperature and return water temperature.

    Make sense?
  10. surfbug

    surfbug New Member

    Jan 12, 2007
    yeh, that does help....

    I have the little fins...........baseboard heating....no big radiators...

    "Every system is optimized for a desired heat drop between source water temperature and return water temperature."

    is this done automatically>? or just by the design of the system

    everything else you are saying makes sense.....


    another thing,

    am I gonna cause any damage if I use kero or deisel in the burner, if I run out?

    like 5-10 gallons........I have done that just wondered if it makes a difference...


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