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  • #16
    Re: Honeywell Low limits and boiler water temp

    I have a Crown model ABF-EID, 4 sections, cast iron exchanger, 105 MBH input and 85 MBH output. It sounds like we have similar setups as I have old cast iron radiators too set up within lots of vertical living space (3 story row house) utilizing gravity. And yes, I don't have a problem heating up the house, but it really takes a while, especailly in the morn. With regards to the aquastat, it only has the high limit setting wheel with a default low limit of 15 degrees less than the high limit, but my water never gets hot enough within the cycles to reach the high/low limits as the aquastat only works when the thermostat is calling for heat. Thus I end up with a low temp of 90F at the start of a firing cycle and 135-140F at the end.

    So, my question to FINER9998 is do you have some kind of bypass set up at the boiler to keep the water temp high, an aquastat that works with or without a call for heat, or perhaps a combination of both? Thanks!

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    • #17
      Re: Honeywell Low limits and boiler water temp

      While we wait for FINERS remarks, may I ask what your thermostat setback is during the night?

      5 degrees?

      10 degrees?

      More?

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      • #18
        Re: Honeywell Low limits and boiler water temp

        anwhite80...for the record, the owners manual for the type of boiler you specify you have states that you have a forced water system and not a gravity feed system. gravity feed hot water systems have no circulators, relying instead on the thermal quality of heat to rise and cold to fall as its means of moving heat from the boiler to the radiators. gravity feed HW systems are like giant tea kettles (which do not produce steam) in that as the boiler heats the water, the hot water rises through the supply pipes and returns to the boiler through the return pipes as it cools. while these systems are very quiet, my experience with them is that they are very slow to provide heat.

        i do not have a bypass anywhere in my system. the boiler relies soley on the aquastat to determine how hot the supply water should get. it will heat to 185 deg, roughly my high limit setting. there is one caveat to this last statement i would like to add. i added an intellicon hw+ to my system. its purpose is to regulate the boiler firing cycles to optimize hot water utilization. unless there is a call for heat, my boiler does not fire.

        our configurations appear to be similar in that when i set back at night, the boiler water temp. can get down to 75 to 90 degs. whenever the thermostats are not calling for heat. we have the same aquastat so they should both heat to a high limit and refire when the water temp. drop signals boiler refiring, again assuming a call for heat. you might try raising your high limit so the boiler sends hotter water to your radiators when there is a call for heat. this would probably help heat the structure faster.
        there's a solution to every problem.....you just have to be willing to find it.

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        • #19
          Re: Honeywell Low limits and boiler water temp

          I set back my thermostat 5 dgrees at night to 60F at 10:00pm. During the week, the thermostat is set at 60f from 10pm to 4pm the next day. From 4pm to 10pm it jumps to 65F. During weekends I have it at 65 from 8am to 10pm all saturday and sunday.

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          • #20
            Re: Honeywell Low limits and boiler water temp

            Originally posted by bigPipe09 View Post
            Do you throttle the ball valve, or leave it full port?

            I also add a temperature gauge to the return side of the piping so that I can adjust (with the ball valve) the average return temperature.

            Bringing water below 140 degrees back to the boiler will cause all sort of problems. Maybe not today but sooner than later.

            The High limit temperature makes no difference at all except that it sets the maximum temperature of the boiler. It should ideally be set at the maximum required temperature to heat the house to the thermostat set point and that depends on the heat loss of the envelope. For copper fin tube baseboard temperatures are usually set at a maximum of between 180 and 210. There are charts that list the btu\hr output for various manufacturers baseboard. The same information is available for cast iron baseboard as well as radiators. Again though, if the radiation is doing it's job the boiler may never reach high limit during normal operation. Think of the high limit as a safety control not an operating control though it can be. Low limit controls are typically used for boiler having a tankless copper coil for making domestic hot water. In that case the boiler needs to be maintained at a certain temperature in order to supply domestic hot water to the faucets. Again this control is not normally used to control the heating circuits. If you want controls that change the but input fronm the burner (oil or gas) then you need a totally different kind of heating plant called a Modulating (condensing usually) boiler. Remember that even the Tekmar and Intellicon modulating controls only adjust the maximum operating temperature of the boiler, not the input of the fire itself. Is all that confusing enough. Hope not. It's what they pay me for.
            sigpic

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            • #21
              Re: Honeywell Low limits and boiler water temp

              Just to clarify for FINER9998...you are right, I incorrectly stated I have a gravity system when infact I have forced hot water with the help of a taco circulator. I was just thinking "gravity" in terms that I have a lot of vertical space where cool water will come back down on it's own.

              And, after cranking up the heat to 75 from 60, and setting the high limit at 140 (lowest setting) on Aquastat, I was able to confirm that the aquastat is working correctly as the boiler shut down at about 140, pump continued running, and about 20 min later it fired back up again when water temp dropped around 15 degrees. So everything runs properly, but the problem still remains that my water temp never gets hot fast enough within the cycles and thus I'm nowhere near a good high limit of 180F. I reckon if I had my thermostat set at 90 all the time I could achieve this...but I think that might be a bit too warm for me...!

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              • #22
                Re: Honeywell Low limits and boiler water temp

                that's because the aquastat tells your boiler to stop heating water once the boiler water achieves a temperature of 140 degs. if the high limit on the aquastat were raised to 165-170 degs., and you conducted a similar test to the one you just performed, the boiler would not stop firing until the boiler water temp reached 165 - 170 degs., it would refire, assuming a continuing call for heat, at between 150 and 155 degs. i would also expect that the house would heat up faster. as NHM notes, the high limit is a safety feature. for a given heat load on any given day, the boiler could stop firing before the high limit temp is reached. but if the high limit is set too low, the water coming out of the boiler could be at such a temperature as to be inadequate to overcome the structure's heat load.
                there's a solution to every problem.....you just have to be willing to find it.

                Comment


                • #23
                  Re: Honeywell Low limits and boiler water temp

                  I realize how the high limit for the aquastat works (I just turned it down to 140F as an experiment to see if it would shut down/if it was working properly), but the problem is that with my thermostat normally set at 65, that call for heat is never lasts long enough (usually lasts about 45 min) to get the boiler temp up, not even to 140! It usually gets up to around 135 or so and then shuts down as the call for heat is satisfied. I could set the high limit at 140 through 220 and it would never make a difference because of the high volume of returning cooler water entering the boiler. That's why I think I need the bypass or an aquastat independent of the call for heat, or a combination of the two. Hope this all makes sense! And again, I really appreciate all of the input on this site! Really good stuff--I'm a new homeowner and this past year has been quite an education...

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                  • #24
                    Re: Honeywell Low limits and boiler water temp

                    have you tried contacting crown? they should know their boiler and could hopefully advise you once they know the quantity and type of radiators you have. when i reviewed the owners manual for the boiler you indicated you had, there are two diagrams for bypass set ups based on the configuration of the circulator relative to the boiler.

                    http://www.crownboiler.com/manuals/c...20ABF-EID).pdf
                    there's a solution to every problem.....you just have to be willing to find it.

                    Comment


                    • #25
                      Re: Honeywell Low limits and boiler water temp

                      Hey, thanks FINER9998! I do indeed have that manual printed out but I never noticed the section on the bypass. This is actually what NHM was talking about earlier. I'm just surprised the installer didn't include this bypass when he put it in 8 years ago! I think come this spring I'll have a plumber set one up along with total system flush and burner cleaning.

                      For now I noticed there are ball valves at each of the 3 return lines to the boiler--I think I'll try turning one off, thus blocking return flow by 1/3 and decreasing the overall mass of water in circulation and increasing flow speed on the open 2. I bet my boiler will heat up pretty fast!

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                      • #26
                        Re: Honeywell Low limits and boiler water temp

                        In case anyone was curious I tried shutting off one of the 3 return lines and, indeed, my rads heated up 30% more quickly and the boiler got up to about 160. On the next cyle I closed 2 of the 3 returns, leaving the pipes that operate the 4 rads (12 all together) in the living spaces open and I'd say they heated up about twice as fast and got super hot while the boiler got up to 180 and within a much shorter cycle. It's amazing how longer a properly heated radiator will keep it's heat! So, I'm thinking I will keep it like this for the winter, with 2 of the 3 lines closed, as the open lines heat up the living areas on the 1st, 2nd, and 3rd floor front section of the house. By manipulating those return line ball valves I'm able to turn the house into 3 vertical zones more or less, and I really don't care if the rest of the house is 15 degrees colder.

                        Is there anything wrong with keeping those lines closed as in a chance of pipes freezing? THe cold part of the house is nowhere near freezing, but probably in the mid 50s or something.

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