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Buderus GB142 Settings problem

Hulka Member Posts: 3

I'm really hoping that someone here might be able to help me out with something that's been bothering me. I am concerned that my heating system is not configured properly.

First, here are the specifics:

Home Details

Location - Connecticut

Home style - Cape (single floor living space)

Build date - 1957

Sq. Ft. - 1,200

Insulation - avg. for build era

Windows - all replaced in 2005

Monoflow system with Cast Iron baseboard radiators.

Heating System (new in 2009; replaced the house's original boiler)

Buderus GB142 24/30 with AM10

Fuel Type - Propane

Zones - 1 (Domestic Hot Water is heated separately with Rinnai tankless)

My problem is that the installer had very little experience with these Buderus mod/con models and had only installed a few others before mine and admitted that properly setting these units up can be tricky. He did say that my radiators would work extremely well with this type of boiler. To his credit he did do a good job on the installation and made several trips out to try and dial in my unit, but to no avail. I spoke with a propane installer on an unrelated matter and mentioned my concerns about my Buderus. He confirmed that not only are they tricky to dial-in for maximum efficiency, but that he doesn't know of anybody in Connecticut who knows how to do it!

We keep our thermostat at a constant 67 degrees. The unit seems to run almost constantly. For example at night, When it's in the 30's, I'll hear the thermostat click and then I hear the Buderus start running. After about 5 to 10 minutes I'll hear the thermostat click again (which I assume signals the start of the purge) and then about 5 or so minutes I hear the Buderus stop completely. After 2-8 minutes I hear the thermostat click and the whole cycle repeats itself through the night. I also go through what seems to me to be an awful lot of propane.

I don't know if this helps, but after the thermostat was inadvertently set to 63 degrees, it took well over 8 hours to raise the inside temp to 67!

My questions are:

Are there special settings for the old-fashioned cast-iron radiators vs. modern finned radiators (I seem to remember reading something to that effect)?

What should the AM10 control point settings be (approx.)?

Is the operation I described normal?

I hope I didn't leave anything important out. I could really use some help/guidance on this. I haven't gotten a good nights sleep during the heating season since it's been installed.

Thank you so much!



  • icesailor
    icesailor Member Posts: 7,265

    I've never installed one of these. So, I'm not familiar with them. Others here may say more. I think the GB142 is a MOD/CON gas boiler. If so, The "clicking" you hear from the thermostat is because it is an electronic digital thermostat. The "click" is the thermostat recycling and checking the temperature. If you have outdoor reset where the outside temperature "sets" the inside temperature, the boiler is maintaining a temperature of the water to a level that will keep the house at the temperature you set it at. If this is so, when you turned down the thermostat, it was the same as raising the outside temperature except that the boiler controls don't know that you did that. Because the boiler doesn't know to raise the system water temperature, it will not raise the temperature in the house.

    As far as how well it is running, I'm sure that by now, there are a few people around that know how to dial these in.

    If it is a modulating boiler, you understand that when it is running, it may be firing at its lowest fire and just jogging along. It sounds normal to me.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Setting up a mod-con.

    I have explained a few times here how I set mine up. I am not a professional, but I know more about these things than my former contractor who recommend the boiler and installed it. He just left it set up with the factory defaults, which would have given enough heat, but actually produced water too hot for the house, and since most of the house is on a slab with copper tubing in it (small Cap Cod house in New Jersey), the house temperature diverged wildly from the thermostat setting. Like +|- 3 degrees F which is seriously uncomfortable.

    I assume your unit has outdoor reset.

    If your unit runs almost constantly, and heats your house to what you have it set at, I would say you are doing very well. If it never shuts off, it means it is just barely keeping up with your heat load. That results in maximum condensing. My aim is to set mine to run 18 hours a day, at least when it is cold out. That allows it to run over 18 hours a day if it is very windy or something like that. This no matter what the outside temperature is. The hard part is setting up the reset curve(s) to match the load of your house at all the usual outdoor temperatures. But if your house is the right temperature at all outside temperatures, that is half the battle. Then you want to make the boiler run as long as possible, and you do that by diddling the reset curve. Or, preferably, have your professional do it. I tried to do it first by calculating from the heat loss calculations for my house. This turned out not to be accurate enough, so I just diddled things for an entire winter and got very close. MY downstairs runs about 18 hours a day when it is very cold out, but only 8 hours or so when it is above freezing outside. So I have a little way to go. The reason you want long run times is because you can get them only with the lowest possible water temperatures. If they are too low, you will not get enough heat. So it is an artistic thing.

    My boiler is a little oversized, so it will not modulate as low as my house sometimes needs. If the thermostat is calling for heat, the boiler will cycle more rapidly than desired. There are several ways to deal with this, but I do not want to put everything into one posting. And since my boiler is different from yours, I would have to guess and someone else on this Wall probably has actual experience with setting one of yours up. Hopefully, someone who lives near you.

    If your thermostat is turning on and off every 10 minutes, that is pretty often. My house is on a slab with radiant heat in the slab. So I set my thermostat to do one cycle per hour. Out of the box, most thermostats seem to be set to 6 cycles per hour, and I find that annoying. If you have all fin-tube baseboard, you might want to set the thermostat to 3 cycles per hour. I have no experience with cast iron baseboard. I would think you should try the range of 1 to 3 cycles per hour on that thermostat.
  • Hulka
    Hulka Member Posts: 3

    Thanks for the replies, but I am a bit confused. since my unit was always capable of getting the house up to temp at the default settings, should I return the AM10 (that's my outdoor reset, yes?) control points to the default values (which are about 8 degrees below their current values)? And the desired result is a boiler that runs constantly? That seems counter-intuitive to me, but I am clearly mistaken in my idea of how these should operate. I don't even really understand what it means to say it is 'condensing'!
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    It pays to be there.

    It is really tough to do this by Wall posting. And remember I am just a homeowner, not a professional heating expert. And that I have never seen a Buderus condencing boiler, though I have glanced at its installation manual and the AC 10 manual.

    I think what you should do, before you do anything else, is to stop and think about your system (it sounds funny to say it this way, but I hope you get what I mean). Have a clear picture in your mind of what you have, and what the parts are supposed to do.

    The AM 10 is the outdoor reset controller. I assume it is installed and wired correctly. If you look at Figure 9, page 10 of the AC 10 manual, you will see a typical reset curve. Your task will be to set points A and B correctly. Perhaps the defaults are a good place to start. But you have to have a plan to get the points right, or it will be a never-ending process.

    By the way, you might want to diddle the cycle rate of your thermostat down from 6 per hour, suitable for forced hot air systems to at most 3 cycles per hour (suitable for copper baseboard systems), and perhaps 2 or 1.

    Decide on the range outdoor temperatures you want to use. To start, I would pick the design day tempreature for the lowest point (or maybe a little bit lower) for point B, and the temperature of the warmest day that you want to heat as point A (if you set your thermostat to 67F, you would surely pick a temperature lower than this for point A).

    Now those two temperatures do not define the curve, because it takes two numbers to define each of those points, and we now have just one each. The second number for each is the temperature of the supply water to your house at those temperatures. You "should" be able to calcualte those temperatures if you know your heat loss at those outdoor temperatures, and the exact heat transfer you can get at 67F from your cast iron baseboards. I put should in quotes, because I found my heat loss calculations had too many assumptions in them for this. They also do not count heat gain from sun through the windows or the heat generated by my computers (quite a bit), and so on. So if your house is comfortable, you might as well start with whatever you have.

    About condensing boilers. To get high efficeincy from a boiler, one trick is to let the water vapor produced by burning gas to condense into water. If you could condense all if it, you might get 11% or so more use out of a therm of gas. You will not get that much, but you might well get 94% of all the energy you deserve instead of only 86% or so. To get the higher efficiencies, you need to have the water returning to the boiler as cool as possible; certainly less than 130F. A great way to ensure that is to not put more than that into your system, since it will come back cooler than it goes out. If your baseboards can put out enough heat, that is. If you are lucky, they put in too much baseboard, so you can run lower temperatures, but unless you are a nut like me, you will not wish to add some just to get the temperatures down. Even if they did not put in oversize baseboards, perhaps you improved the insulation or the windows or both, and this reduces the heat necessary, allowing lower temperatures.

    So what outdoor reset is for is to get you returning water temperatures as low as possible and still heat your house. The higher temperatures are needed only on the coldest days, so my guess is that your system may not condense on the coldest days. But most days are warmer, and you should get condensation then.

    So on a "warm day", notice how many hours a day the thermostat calls for heat, assuming the house is warm enough that the thermostat turns off sometimes. My view is that you want it to call for heat about 18 hours. Some people think it should call for 24 hours. Others say much less, or wisely, say nothing. My theory is if it calls for more than 18 hours, chances are you are to cold and will get into trouble on exceptionally cold windy days, and if you are much less (say less than 12 hours) the water is too warm. But basically, if you get a string of warm days, you can set point A.

    Then wait for a cold day, preferably the coldest day of the year, and see if the house is warm enough. If not, raise the boiler tempreature for point B to get the house warm enough. Then fine tune that to get 18 hours run time. Each time you change one of those temperatures, I would wait 24 hours to let things stabilize and see where you want to go. It is tedious, but not difficult. It would be a lot easier if you could adjust the outdoor temperatures.

    I am lucky that I have a Honeywell CT-3600 thermostat that tells me the number of hours and minutes it has called for heat today, yesterday, and since I reset it. I do not know if they still make it.

    Remember my recommendation, though. Do not do anything until you have thought about it enough to be sure you understand it. Otherwise you wil ljust drive yourself crazy.
  • meplumber
    meplumber Member Posts: 678
    I have installed more of these than I care to count.

    I need a little more info.  Feel free to email me using the "Contact this User" tab and I will see if I can help you out.
  • Hulka
    Hulka Member Posts: 3
    You Guys Rock!

    Still working on my problem (if it is actually a problem) thanks to a couple of you guys. Just wanted to say how much I appreciate you sharing both your experiences, knowledge and wisdom. I've learned more here about mod/con boilers in the last 48 hours than in the last few years!

    For the first time, I feel like I am actually on the right path. You have my respect and appreciation.

    Thought you should know how much this means to me.

This discussion has been closed.