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  • Honeywell Low limits and boiler water temp

    Hi,

    I'm a little bit stumped with my boiler's operation. I have a 7 year old Crown nat gas hot water boiler with an input of about 100,000 btu's (I'm guessing that's around 80,000 btu output?), coupled with a Honeywell L8148E aquastat. Everything runs fine, but after reading how most other people's boilers run mine seems a bit different. There is no low limit setting on my aquastat so the boiler, circulator, and damper only operate when my living room thermastat calls for heat. Because of this, the temp of the water never gets above 140F just after firing and falls to around 90F just before the next cycle starts, and the cycles last quite long between 45min to 1.5 hours depending how many degrees of difference I want. It seems like most other boilers have a low limit setting that keeps the boiler water temp higher thus creating shorter firing cycles. So I'm wondering if this is normal and efficient or not. I understand that higher efficiency is achieved once the boiler has been firing for a while, so fewer cycles may make sense, but the low water temp seems off. PSI looks to be around 15- 20 range. Most of my friend's radiators get super hot fast but mine get hot very slowly. I should also mention I live in a 1500 sq. ft 3 strory row house with upright radiators. Could my burners be dirty and not achieving max heat? I don't think the boiler has been serviced for a few years. Anyway, any advice would be very welcomed. Thank you!

  • #2
    Re: Honeywell Low limits and boiler water temp

    It is very efficient. The big question is whether or not your home heats to the temperature set at the thermostat. 90 degrees is too low a temperature for the returns so a bypass valve should have been installed.
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    • #3
      Re: Honeywell Low limits and boiler water temp

      Yeah, I assumed it was running efficienly with the longer cycles but I am still curious about that low water temp. Would it make sense for me to increase the swing option on my thermostat? That would increase the cycle lengths even longer and get the temp up in the process. It currently fires up at 64 and drops off at 66, that 3 degree swing is the default setting.

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      • #4
        Re: Honeywell Low limits and boiler water temp

        Nope, changing that setting won't effect return temperatures at all. You really need a bypass to bleed some of the supply water back into the cold return water to keep the boiler from sludging up. I usually use a 3/4 line with a manual ball valve, but you can get fancy and use a thermostatically operated valve with aquastat control if you want to.
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        • #5
          Re: Honeywell Low limits and boiler water temp

          Thanks for the advice on the bypass. I should also mention that one of the first floor radiators close to the boiler in the basement only gets lukewarm at best on top and remains cool on the bottom, suggesting it is filled with sludge. Could this mean there may be sludge throughout the entire system, even in the boiler itself and if so could that be creating the low water temp and very long cycle times? I'm also not sure if my expansion tank is working at it never feels warms when expanding hot water should be filling it. Perhaps it is waterclogged. Anyway, thanks for the adivce!

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          • #6
            Re: Honeywell Low limits and boiler water temp

            More likely air than sludge.
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            • #7
              Re: Honeywell Low limits and boiler water temp

              I don't think it's air I've bled it and there's always water coming out. Also, if air was in there wouldn't it be warm on the bottom and cold up top, just the opposite?

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              • #8
                Re: Honeywell Low limits and boiler water temp

                That boiler is no where near old enough to have a significant about of sludge built up. It may have some but not enought to affect it's performance. The expansion tank never gets hot.

                You mentioned a 45 to 1-1/2 hr cycle time. Is this the boiler firing or boiler off time?

                90 degree temp in the boiler is bad news. That boilers' minimum temp should be well over 120 degrees.

                The L8148E lowest setting I thought was 140. Do you have a separate low limit controller?

                Have it serviced by a professional

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                • #9
                  Re: Honeywell Low limits and boiler water temp

                  Yeah, the boiler is quite young, about 8 yrs old or so, but some of the radiators are as old as my house, about 100 years, and connected with black pipe (that's why I thought it could be sludge). The 45 min-90 min cycles are the boiler firing time. If it's around 35 degrees F outside it will fire for about an hour and then sit quiet for about 2 hours until the next cycle starts. It only fires and circulates when the thermostat calls for heat. Nothing runs when there is no call for heat (well, except the pilot of course).

                  At the end of a firing cycle, boiler themometer reads about 140. Just before the next cycle starts, the the thermometer reads around 90. PSI ranges from 15-20 or so.

                  I took off the plate of the aquastat and found only one dial in the back and tried turning it up from 180 to 200 but it made no difference. From what I understand, that dial controls the high limit. I saw no other dial controlling low limit. Any chance I could have dirty burners? Thanks for your input man!!!

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                  • #10
                    Re: Honeywell Low limits and boiler water temp

                    are any of these the boiler you are asking about:

                    http://www.crownboiler.com/products/res_gas/index.asp

                    also, the l8148 aquastat has a high limit only setting with a preset low limit differential which i believe is 15 deg. if the high limit is set for 160, the boiler, once receiveing a call for heat, heats up to that temperature and turns off. the circulator should keep working as long as the thermostat keeps calling for heat with the boiler refiring once the boiler water cools to 145 deg. (160-15=145). here is some info on the l8148e:

                    http://customer.honeywell.com/Techli...0s/60-2278.pdf

                    i'm no heatinig pro but it sounds like the high limit is not set high enough if your boiler water never gets over 140. is it a single or multiple zone system? in my 5 year old HW nat gas fired 4 zone heating system, my aquastat is set for 185 as i have two zones that are cast iron radiators and two zones that are copper baseboard. the only time my water temp. is around 90 deg is when the thermostats are set back overnight to 60 degs and the only heat produced in the boiler is from the standing pilot light. if you check out this thread, you'll see this topic has been discussed, to some extent, previously:

                    http://www.ridgidforum.com/forum/sho...quastat&page=3

                    hope this helps.
                    there's a solution to every problem.....you just have to be willing to find it.

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                    • #11
                      Re: Honeywell Low limits and boiler water temp

                      What you have is a relativly low mass boiler driving a high mass radiation system. The boiler high limit should be set around 200 but most likely during normal cycles it will never reach it because there is so much cold mass returning to the boiler. In these cases (and it's very common now) a bypass loop between the feed and return is necessary. This loop can either be operated with an aquastat and zone valve (or circulator) or it can be done manually with a simple ball or gate valve and a thermometer to monitor return temperatures. I would rather see fairly low and consistant water temperatures than high feed and very low return temperatures as the latter can cause thermal shocking. However the former is not good either because it can and does lead to combustion temperatures that are at or below the condensing threshold and can lead to premature chimney and collector failure. The installer should have known better when the system was put in.
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                      • #12
                        Re: Honeywell Low limits and boiler water temp

                        Thanks for the links above. The previous ridgid forum link brought up a new angle regarding a spring loaded stop located on the high limit dial which is supposed to be depressed when changing the limit, but my aquastat didn't appear to have this stop, just the dial with a spring behind it (honeyell L8148 E1257). Although, it was quite difficult to look back there since that side of the aquastat is about an inch from the boiler! Like earllier, my dial turns freely but this has no effect on the boiler. Still stumped....thanks.

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                        • #13
                          Re: Honeywell Low limits and boiler water temp

                          The more researching and thinking I'm doing leads me to think that "NHMaster 3015" is correct in that I need some kind of bypass loop set up to deal with my high mass system. It sounds like my aquastat is designed to kick in with the 15-20 degree low limit default differential, BUT only if the thermostat is calling for heat. I was under the impression that my aquastat should be regulating water temp independent of thermostat requests but it sounds as if the Honeywell L8148E only kicks on the low limit when calling for heat. With my high mass system, the return is cooling down the boiler before it can ever reach a high limit, so the aquastat's high and low limits are rendered obsolete. So, tomorrow morning I'm going to set the high limit at the lowest setting (140F), crank up the thermostat, and I bet the boiler will shut down with only the pump running when it reaches 140. And later I should see the bolier fire up again at 125 or so as long as I have the heat still cranked. At least this will be evidence that my Aquastat is running correctly, but unfortunately I'll most likely need a plumber to put in a bypass!
                          Last edited by anwhite80; 01-11-2009, 12:01 AM.

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                          • #14
                            Re: Honeywell Low limits and boiler water temp

                            which model crown do you have? is it a stainless steel or cast iron? most of the boilers on the crown web site are cast iron heat exchangers, which i am interpreting to be high mass boilers.

                            before i changed my boiler 5 years ago, i had cast iron radiators and a 50 year old 90M btu nat. gas fired boiler feeding a gravity feed hot water system. the overall mass of the radiators far exceeded the mass of the boiler, and the house heated even on the coldest days. being a gravity fed system, it just took several hours to realize an 8 degree heat rise from night time set back to day time set up.

                            i agree that the aquastat water temp should be set higher than 140. when i had all CI radiators, an aquastat temp of 165 provided what appeared to be good operating cycles and efficiency.
                            there's a solution to every problem.....you just have to be willing to find it.

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                            • #15
                              Re: Honeywell Low limits and boiler water temp

                              Originally posted by NHMaster3015 View Post
                              Nope, changing that setting won't effect return temperatures at all. You really need a bypass to bleed some of the supply water back into the cold return water to keep the boiler from sludging up. I usually use a 3/4 line with a manual ball valve, but you can get fancy and use a thermostatically operated valve with aquastat control if you want to.
                              Do you throttle the ball valve, or leave it full port?
                              West Trail Mechanical Ltd
                              Service. Commitment. Expertise.

                              www.westtrailmechanical.ca

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