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Heat curve issue

boulder1 Member Posts: 4
I have a 10 year old munckin contender. Always kept the house warm until the last two years. Ive had regular service during this period so folks have had the chance to monkey with the boiler. Indoor temps now max out at 67-68 when outdoor temps are in teens. Installer/maintenance company said heat exchanger is failing because of mineral build up and suggested a new boiler. Had questions about installer on other issues (200% markups on parts, quality of work issues, potential integrity issues). I noticed boiler never gets above 140 F. I checked vision 1 settings and the heat curve was set so min/max outdoor temps were both 32 F and max temp was 140 F. Outgoing water temp was 139-140. Changed settings so that boiler water temp could hit maximum (180) at outdoor temps below 32 F. Boiler fired to near 180 and house got warmer. Problem is that outdoor temps rose also that day so I don’t have good data on whether I resolved yet. Questions are: (1) is there any good reason to set the heat curve the way I described (min/max temp both 32 highest allowed water temp 140)? Seems like the settings cut off the boilers ability to deliver btus at full potential. With low outdoor temps, an older house, and a meaningful limit like this I’d imagine the boiler wouldn’t be enough to meet loads even if the installer included generous extra capacity; and; (2) any reason I shouldn’t keep the new setting? what is an appropriate heat curve for this unit? I’m guessing I’d need to do a loads analysis or figure it out via trial and error. Trial and error is fine so long as my wife and 1 year old are no longer freezing...

Thanks in advance


  • Zman
    Zman Member Posts: 6,454
    The outdoor reset curve allows the boiler to run at lower temps during warmer weather and saves you money. The correct settings depend on the construction of the house and type of radiation.

    When someone sets it the way yours was, they just don't want to deal with it and are over riding the controls.

    Tell us more about your system. Pictures are helpful.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • neilc
    neilc Member Posts: 1,208
    yeah, add in where you are,
    by your name I guessing Colorado.

    Your boiler manual and the controller should allow you settings for high and low settings for both heating water (HW) temps, and outdoor air (OA) temps,

    Does the boiler show an OA temp in the display also?
    Hopefully the installer has a sensor already installed.
    if so,
    You might end up with high OA setting around 60~65, low OA around 0 (zero) or whatever is appropriate for you location,
    and the high water temp, when OA is lowest, can stay at 180 for now. You will want to adjust that down till it just keeps up on your coldest night for best efficiency.
    Your low water temp, when OA is highest, will depend on your system design.
    It might be as high as that 140, or you may be able to dial it down also,
    but we need to know the system to better advise.
  • boulder1
    boulder1 Member Posts: 4
    Understood re: purpose of the curve. House is two story 1960s ranch locates at 5,900 ft in Colorado. I would classify it as poorly insulated by current standards with average r-15 in exterior walls and attic (yes, this is on the list of upgrades). House has four hydronic baseboard heat zones and is approx. 2300 sq. Ft. Boiler is munchkin contender mc120 (18-120k btu) which runs heat and supplies hot water to 80 gallon tank. Boiler was installed in 2009 and worked fine until last winter. Boiler has had annual maintenance. Boiler replaced an old diesel furnace from 60s that obviously didn’t modulate temps. Older furnace and (before problems) the munchkin both produced pretty hot baseboards. Lately baseboards were warm but not hot, which led me to investigate the issues outlined above. Anything else I can tell you?
  • neilc
    neilc Member Posts: 1,208
    how about a picture of the boiler, and the circulator(s), and the piping around it?
    one picture showing the whole system.
    and one of your baseboard.
    Did your trouble start after one of the tuneups?
    maybe the settings were "adjusted", and need to be reset.
    does the boiler display show OA temp?
    and do you have your manual?
  • ratio
    ratio Member Posts: 2,729
    Note that when you utilize outdoor reset, you will (hopefully) find that you can heat the house comfortably without the baseboards ever being more than warm until it's positively frigid outside. If you want the baseboards to be hot, you'll need to disable the ODR & run the system more like it did with the old boiler.
  • neilc
    neilc Member Posts: 1,208
    do you know if you have the Vision controller installed?
  • boulder1
    boulder1 Member Posts: 4
    Here is the boiler and a typical baseboard radiator. Yes, the boiler measures OA and has a sensor installed. System uses the vision 1 controller. Trouble started after tune ups, but not immediately. The boiler works well enough unless temps fall below 20 F. My sense was that I should set the high water temp (when OA is say 25 or below) to 180 and then experiment with the water temp when OA is higher. My guess is I could lower it to 140 (previous setting which worked) or maybe lower. My guess is that a tech messed with the settings during maintenance and caused the current situation. But who knows? I do know boiler/baseboards used to get hotter when it was very cold. Seems like that changed over the past winter. Baseboards are now back to being very warm.

  • neilc
    neilc Member Posts: 1,208
    your tech "tuned it" when it was warm and you wouldn't notice it till now and it's being cold.
    You just got to set back in a proper reset curve.
    Do you know your design temp for Boulder?
    that's your low OA setpoint, and I'm thinking 180 for the HW.
    try high OA at 65, and low HW at 100.
    These can be tweaked but it's a good start.

    What's that drip stain on the boiler cover?
    condensation leaking back from the PVCs?

  • Voyager
    Voyager Member Posts: 256
    edited December 2018
    Curious as to why you suspect integrity issues.

    It seems to me that you likely have found the problem. Most likely the radiators were designed for 180 water at design conditions. Limiting the temp to 140 would seriously compromise the fin tube output. For example, for one type of fin tube the loss in heat output is nearly 50% going from 180 to 140.

    The question now is: Was the ODR curve screwup due to ignorance or malice? It could well be simple ignorance as many seem to have a hard time comprehending the very simple ODR concept. However, given they they suggested you needed a new boiler, I would not rule out malice.
  • ratio
    ratio Member Posts: 2,729
    Never attribute to malice that which can be explained by incompetence.
    BrewbeerCanuckerdelta TDan Foley
  • neilc
    neilc Member Posts: 1,208
    malice, incompetence,
    sometimes I'm a, "abrupt"
    call it what you will,
    you're here asking about it,
    did you get the reset back in there ?
  • Zman
    Zman Member Posts: 6,454
    With a setup like yours, it will be a trial and error experiment. I would try it at 180 when it is 0 degrees outside and 130 at 60 degrees outside. That would give you 155 at 30 degree outside temp
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • boulder1
    boulder1 Member Posts: 4
    Thanks to all of you for your help. I can’t prove intent on this one - but I do assume that if I can figure the issue in 20 minutes with the manual then a professional should be able to do. who knows? Another case of it paying to understand the stuff you own on a basic level. I do know my house is now comfortable, and I didn’t have to buy a new boiler to made it happen, so I’m happy.
  • Gordy
    Gordy Member Posts: 9,530
    If everything was fine on a 10 year old boiler until this year, then something changed.

    Could be any one of the following.

    In 9 years you have not experienced that low of an outdoor temp to create the inability to meet the load.

    The outdoor sensor could be failing, or failed.

    Who ever did the servicing tampered with the settings.

    If serviced ritually, and make up water is not constantly added to the system I can’t see that the HX would have mineral build up.

    Is the same company servicing this boiler that installed it?

    You said the contender does domestic hot water. Is it meeting the demand?

  • delta T
    delta T Member Posts: 825
    Side note, is there a plug in vent on your backflow preventer? That is a safety device and should be replaced if the vent is leaking....

    I used to live and work in Boulder, my father started the business 40 years ago. We are now in far southern Colorado. If you need recommendations for service companies in Boulder PM me.

    Are you in town or up in the mountains, I assume mountains as you had an oil system before this. Are you on a well or on one of the city supplied water districts west of town?

    Sounds to me like the tech adjusted the reset curve either intentionally through ignorance, or by sheer accident. I wouldn't jump to unethical behavior right away because of a "200% markup on parts" Boulder is an extremely expensive place to do business. Please understand that the prices you can see online for parts are likely the same or even less than what we can buy them for through wholesalers The difference is that when we buy parts through a wholesaler who we have built up a relationship with, if there is a problem, it gets dealt with quickly and without fuss, usually on the same day. Online retailers, or Home Depot, not so much.
  • SuperTech
    SuperTech Member Posts: 1,579
    Why is that garden hose hooked up to the boiler?

    That oil unit must have really been running poorly to get the boiler room that dirty.
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