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Gas Fired Boiler running constantly during the summer

I became a new home owner in 2023. I have been trying to determine what in my house is utilizing and driving my natural gas bill.

I have a gas fired boiler connected to an indirect domestic water heater. The boiler also heats the entire home radiators via hot water. There are two separate hot water loops for baseboard heating in two other zones. And there are two hot water radiant floor heat zones. The house also has a dedicated return domestic hot water recirculation system.

During the summer the boiler was using about 10CCF per day! The heating was not on but the house was unusually warm even into the fall when temperatures fell into the 50s (and everyone else's house was getting cold). My initial thoughts were the recirculation line (uninsulated hot water supply and return) were effectively acting as heating elements throughout the house. I shut off the pump and closed the valve (just to verify there was no flow). This had minimal impact on usage (maybe 0.5-1CCF per day).

I noticed that the pump for the indirect water heater seemed to be set to run constantly (maybe the aquastat is bad?) and the boiler supply line in and return from the water heater weren't insulated. I insulated those and saw maybe 1.5-2CCF per day improvement.

I have tried turning off the DHW heater (this turned of the DHW pump) and still find about the same usage. For whatever reason the boiler temp seems to drop from about 170-150 according to the temp gauge and then fires back up. Before insulating and shutting off the recirc system, it did this about every 30 minutes. Since insulation and shutting down recirc, it does it about every 40 minutes. It runs for a couple of minutes minutes which is roughly 0.17 CCF. The boiler system - doing NO heating is using about 6-8CCF/day.

I have run countless tests for the last few months (I enjoy this tinkering type of thing). When no one is home, the heat is off, no hot water usage, no gas fired dryer, aka nothing but DHW it pulls the same amount of nat gas.

It just seems like too much consumption to just keep a boiler between 170-150 with nothing drawing on the heat.

I guess I'm looking to you guys for any ideas. I have no idea intuitively what a possible heat transfer from a boiler to ambient could look like, but this feels like entirely too much. And that explanation doesn't address why my house was feeling warmer when it was still cool outside. I still don't have to run the heat in my house when its about 50-55 degrees F outside.

Thanks in advance.

Somehow I am still utilizing about 7-8 CCF/day with only the hot water calling for heat


  • hot_rod
    hot_rod Member Posts: 21,846
    Typically the indirect call for heat starts the pump and fires the boiler. No reason to keep the boiler hot all the time

    Mis piped you could get flow to the heat zones with a hot boiler, even when you don’t want or need it

    Any other gas appliances?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • TonKa
    TonKa Member Posts: 100
    edited January 30
    Things to check:

    - The low limit on the boiler aquastat is enabled when it should not be.

    - The Indirect WH aquastat is malfunctioning.

    - The boiler is wired to fire continuously and the house thermostats only affect the zone circulators and/or zone valves
  • yellowdog
    yellowdog Member Posts: 144
    More than likely the boiler had a coil in it at some point and the previous owner abandoned it and added the indirect. Whoever made those changes didnt do it right and remove the low limit.
  • newhomeowner2023
    newhomeowner2023 Member Posts: 4
    Thank you all for the feedback. I do think the aquastat on the indirect isn't working. It is set at the lowest setting (120) but the pump is constantly running and the gauge is always over 150. This would make sense since the boiler is kicking on at 150. If the pump to the indirect is always running the lowest I would expect it to get would be 150 since the boiler is always at that point.

    How can/do I change the low limit setting on the boiler? Do I need to be worried about cold start with that?

    Still not sure how this would be heating my house, but all seems like things that are wrong and need to be rectified anyway and then see if it does fix the total nag gas demand for the house.

    Thank you all for the thoughts.
  • newhomeowner2023
    newhomeowner2023 Member Posts: 4
    Only other gas appliances are dryer (barely moves the needle when it runs and we don't run it nearly that often), and our stove/ovens (we don't run a bakery out of our house - typical use once or twice a day - again, barely moves the needle on the gas meter when its running).

    I don't see any mis piping to heating zones...but I am curious if I could be getting gravity flow to the radiators. There isn't a heat trap off the outlet of the boiler before the pipes run off to the radiators. The pump on the radiator system isn't on when it isn't calling for heat. Can a gravity flow push through a pump if its off?

    Boiler doesn't fire continuously - if I'm understanding your comment correctly. It does cycle - just does so with a high frequency.

    There are no automated zone valves (just manual valves on the sides of the radiators - balancing valves?). When the radiator stat calls for heat that pump turns on and the boiler kicks on.

    No idea if the boiler was modified at some point in the past and used to have a coil in it. How would I check to see?

  • dko
    dko Member Posts: 557
    Post photos of the boiler, the controls you can see, and the near piping.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,554
    edited January 31
    @newhomeowner2023 there are so many things that could be driving your boiler to operate when it is not necessary. Can you offer the brand name and model number of the boiler. and any pictures that you can provide that will let us all know what you are dealing with.

    Next is ... Will this be a DIY project to correct the problems you discover. or will you be getting a professional to look at this? Some of the controls systems that are on boilers can be overwhelming even for professionals. Control wiring is an art that few of us can master. Many can make ductwork look nice, many of us can install piping that is a work of art. The controls that connect the burners to the pumps and the zone controllers and mixing valves so everything works efficiently can be confounding for many of us.

    You have high temperature zones and low temperature zones and you are heating potable water with the same burner. if not done properly, you could be wasting valuable energy! Get us more info so we can help.

    And I can't help myself but... your discussion is titled:

    Gas Fired Boiler running constantly during the summer

    You do know this is January, right?
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • newhomeowner2023
    newhomeowner2023 Member Posts: 4
    YES! - I know its January and freezing cold but my head has been wrapped around this non-heating gas usage since it was summer and not having it happen again!

    My general thoughts on DIY vs professional: this boiler is 20 years old and will likely need to be replaced in the next couple of years? If there is a way to do it myself to at least not torch money until the time comes to replace the whole unit and set up, its my preference. There are other issues I will eventually want a pro to address in one fell swoop: one of the zone valves is stuck (can be forced open or closed in manual mode but the electronic actuator can't move it. I took the actuator off the valve and it does work...its definitely the valve), there are almost no isolation valves to replace anything without draining the whole system, some type of zoning on the radiators would be nice, bad aquastat on DWH etc.) All of this can be addressed if the boiler fails in the next few years. Let me know if you think this is the wrong approach, I'm not opposed to bringing in a professional.

    Even if there is a way to manually turn off the low limit on the boiler for the spring/summer/fall and then turn it back on for heating season, that would be preferable.

    I have attached a few photos of the boiler room, there is a lot going on...

    The boiler has two hot water outputs on each side coming off the top. One side feeds the DHW, the two radiant floor, and the two separate baseboard heating zones. The other side feeds the radiators throughout the house. Each side has an aquastat that can be adjusted with a screwdriver, I also took a picture of one of them with the cover off. They are honeywell aquastat l4006a. Why are there two? Can you set two different temperatures? ...sure I'm missing something here.

    Thanks again in advance.

    The boiler is a Burnham 5B - the nameplate photo is included.
  • TonKa
    TonKa Member Posts: 100
    The picture of the aquastat dial is blurred. Best guess is it is set to 170 degrees, which matches the marking on the cover. It's probably the high limit aquastat.

    What is the other aquastat set to?
  • ethicalpaul
    ethicalpaul Member Posts: 5,585
    It sure would remove a lot of complexity to have a standalone water heater...you could even turn off your boiler in the summer instead of heating your house with it in August.
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el