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Buderus with logamatic R 2107

rfrozy Member Posts: 7
Recently moved to a new house. Previously had propane forced air. Now I moved in with a German and have no clue what do with her apparently.

We have a buderus oil boiler with a logamatic R 2107 and an attached Buderus logalux s-120 hot water heater. 2 zones one first and one second floor.

I replaced the manual Honeywell's with two nest thermostats that we received as a gift. I'm struggling to figure out exactly how this system works with the thermostats if it does at all. So here goes...

My understanding of the logamatic is it's basically a programmable thermostat for the heating that does a bunch of stuff for everything else (I'm not worried about hot water that's working great).

Can I use the NESTs with the logamatic? Two wires is all I had. Attached W1 and Rh. Just matched with previous thermostat.

Is there a way to override the logamatic scheduling to just accept instructions from the thermostat for heating.

Heating on average takes about a degree an hour? Is that normal for baseboard radiators? Are baseboard fine and pipes supposed to be hot to the touch? Not just luke warm.

Upstairs gets wicked hot at night around 2 or 3 am (even before nests). However one bedroom is always cold. Any suggestions. I tried bleeding the line upstairs already.

I appreciate the help. We have 5 boys (you'd think that's enough hot air to heat the place) and I'd rather not pay to have someone come out before Christmas. I did some research but it appears to be really difficult to find any information on this thing.


  • Ironman
    Ironman Member Posts: 6,868
    The 2107 is NOT an "on demand" control. In other words, it doesn't turn the burner on because a thermostat calls for heat. Instead, it operates off of an outdoor reset curve which adjusts system water temp based on outdoor temperature. The colder it gets outside, the hotter the water temp in the system.

    The thermostats operate either circulators and/or zone valves which cause water to be circulated upon a call for heat. The 2107 determines the water temp from its ODR curve, the coolest being 104* and the hottest being 194* with factory settings. This is adjustable for different systems. It's the 2107 that activates the burner directly, not the stats. It's European technology and it works well, but most American's minds are fixated on 180* all the time.

    You should NOT use Nest or another type of setback thermostats with ODR. They fight the logic of it. Use a standard thermostat and keep it set at one constant temp to get the best efficiency and comfort.

    Hydronic systems respond much slower than forced air and this is another reason to leave the stats set at a constant temp.

    You may have other issues which are causing uneven heating and I'd recommend that you use the contractor locator above to find a COMPETENT HYDRONIC tech to check your system. If it doesn't list one in your area, post your locale and someone may be able to recommend one.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • SuperTech
    SuperTech Member Posts: 1,792
    Use the nest thermostats as a Christmas gift to someone who has a forced air system. Everything Ironman posted is accurate. That's a pretty sophisticated system, it would take a significant amount of studying for someone inexperienced to set up correctly. If you do hire a pro I recommend using the find a contractor tool available on this site. A technician who isn't familiar with this system could do more bad than good.
    HVACNUT Member Posts: 4,594
    Nix the Nests and start reading.
  • rfrozy
    rfrozy Member Posts: 7
    I really appreciate the help. I will definitely change them out. So if I just turn off any automatic scheduling for the nests that should take care of the problem I created for now until I can buy two regular thermostats? I.E. just make it a dumb thermostat for on demand only no scheduling?

    I've read what I could between the manuals and online and plan to have a tech come in post Christmas to give the whole thing a once over.
    It was an elderly couple that lived there prior to us moving in. Is it possible the scheduling or whatever temps on the controller are just set too low for what we are looking for? Boiler temp looks like it's on average around 140-150. Temps are set to 65 during day and 62 at night 7 days a week (The house temp is the only thing I've changed)? Is it too much for baseboard heating to heat up from 62 to 65? And last and final question the temp the logamatic is set to (65 at 530 AM) does that mean it starts to heat at 530 AM or should be 65 by 530 AM. Trying to get it set right for our schedules
  • rfrozy
    rfrozy Member Posts: 7
    PS I tossed the two regular thermostats I had like an idiot. I don't want to sound like I ignored the advice i hear it loud and clear. Thank you guys so much
  • Noel
    Noel Member Posts: 177
    Look at it this way. The Logamatic chooses a water temperature to (hopefully) exactly match the heat loss of the building at a given outdoor temperature. To increase a room temperature, you need a HIGHER water temperature than the house needs to exactly match its losses. Therefore, the boiler can no longer be running at the lowest water temperature that it can for the outdoor temperature at the time.

    Since boiler efficiency is determined by low stack temperatures and run time, the water temperature is the only variable that you can choose (to lower stack temperatures) by how you operate the system.

    For comfort and maximum fuel efficiency, try to choose a room setpoint that you can enjoy all of the time and set the Logamatic as low as you can and still maintain that room temperature. That avoids the long recovery times with a correctly set up Logamatic.

    Ideally, the zones will run almost constantly at a very low water temperature, when adjusted ideally.
  • rfrozy
    rfrozy Member Posts: 7
    So should I set the dial to Auto or lower it over time? Say keep room temp at 65 and turn dial down to temp that maintains the 65?
  • BennyV
    BennyV Member Posts: 47
    edited November 2018
    The Logamatic 2107 can do some really cool stuff if you know how to set it up properly, the problem is, the documentation is terrible, and doesn't really explain what all the settings do. There are two different ways to operate a 2107 with a system that consists entirely of radiators/convectors (like baseboard or cast iron radiators).

    The R2107 doesn't respond to thermostats, it simply keeps the boiler on a 26-degree differential, with the midpoint of that differential set by the outdoor or indoor reset curve. It has a wire that powers the zone board (that powers the pumps or pump and zone valves) only so that it can shut the heat off when it needs to generate hot water, so you always have plenty of hot water.

    The R2107 also can do some radiant floor stuff with an add-in board, but it's even more complicated, and I'm going to assume that doesn't exist for the sake of this discussion so as not to confuse you.

    Method 1: Outdoor Reset:

    You can use an outdoor reset curve with individual thermostats. You set the outdoor reset curve so that it provides slightly more heat than you need for any given outdoor temperature. There are offsets and schedules and all sorts of stuff designed for a German system that uses thermostatic radiator valves, but in an American system, the curve sets the boiler water temperature, and the thermostats control the individual zones.

    If you set up the curve correctly for an outdoor reset configuration, then the water will be hot enough that your hardest to heat zone will call about 85-90% of the time under normal conditions. You want the water slightly hotter than the zones needs to maintain, so that on a particularly windy day, or if you leave a door open to do something for a while or whatever, the system has a little bit of extra oomph to slowly recover back to the set point or deal with slightly higher loads, since the ODR only reads temperature, not wind and sun conditions, which can influence your heating load. If the zones are well balanced, the others will call 85-90% of the time as well, but in a lot of houses they just aren't, so the other zones may not call as much, and their thermostat will keep them at the correct setpoint.

    Method 2: Indoor Reset:

    This is the Cadillac of high-temperature (not radiant floor) oil-fired hydronic heating systems. It requires an add on called the "BFU room sensor", which I can only assume stands for some sentence-long German word for something. It's an indoor reset control that you put near your thermostat in the hardest to heat zone in the house.

    You would set the R2107 to heavily influence the outdoor reset curve based on the BFU room sensor's input, effectively controlling the boiler on indoor reset, not outdoor reset. The BFU room sensor has a dial on it, but it's something you'd adjust once and leave, it's NOT A THERMOSTAT. Let's say you want the house to be 64F, you'd set the BFU room sensor to 64F, and the thermostat to 68F, and the thermostats in the other zones to whatever you want the room temp there to be, let's say 62F. You CANNOT USE a Nest or programming thermostat in the main zone in this situation, as it will fight the BFU room sensor, and go knows what will happen. You could end up with really hot or cold boiler water, and a very inefficient system.

    The BFU room sensor will control the boiler's heating curve to match the heat needed in the room, using an algorithm programmed into the R2107. If it works as designed, the temperature won't fluctuate more than a degree or two at most during most of the heating season, and the main zone's thermostat will be calling for heat all winter, and never reach it's setpoint of 68F. In the shoulder season, you'd need to use the thermostat to control the temp, say to 65F, as the boiler can only finish it's cycles so low before condensing, so it will always heat to 130F water temp.

    Then, the other zones will have individual thermostats that will call most of the time, but since you have the BFU room sensor in the hardest to heat zone, those will have a little more than they need. In a well balanced house and system, those zones might run 80-90% of the time, in a poorly balanced house, or one where there is a lot of heat that rises up stairwells and cathedral ceilings into the upstairs zone, those other zones may run way less than that.

    Because the BFU room sensor is inside the house in the hardest to heat zone, it's already factored in if it's windy outside, or if it's cloudy or sunny or someone left the door open to let the dog out or whatever, since that affects how much heat the room needs, and that zone should continue on constant circulation all the time, gently replacing just the heat lost. If you improve the insulation, or draw the blinds at night, the curve will automatically drop a little bit, and you can even use the R2107's built in temperature schedule to set back the indoor room temperature at night on a pre-determined schedule, and it will vary boiler temperature to get that zone where it needs to be.

    The other zones are best left at a constant temperature, but you could use a programmable thermostat to vary it a few degrees if you need to for sleeping, etc, just know that with an outdoor reset curve, and especially with an indoor reset sensor on the hardest to heat zone, depending on how well balanced the zones are, it will take a while to heat back up, so if you want it 64F during the day and 59F at night, you might need to have the programmable thermostat switch to 64F several hours before you want it at 64F, and there is little to no efficiency savings in this type of thing, so only do it if you need it colder to sleep and warmer during the day or something like that.

    The R2107 is a pretty neat device, and it can work well for high temperature radiator or convector systems that are oil fired, however, it's very limited in what it can do with more advanced hydronic systems. It has some radiant functionality, but beyond that, it doesn't work well with certain types of radiant systems, hydro-air, or at all with buffer tanks, reverse indirects, etc, etc.

    EDIT: Fixed a typo. I'd also recommend a system with an R2107 to have the most efficient ECM pumps you can get, as constant circulation or near-constant circulation is certainly more efficient for oil consumption, and way more comfortable, but it can suck up a lot of electricity pumping water around.
    HVACNUT Member Posts: 4,594
    Leave the dial on Auto. That allows the boiler to regulate water temperature based on outdoor temperature.
    Check to make sure you have an outdoor sensor connected.
    The switch on the right side should be on Auto also. If theres no outdoor sensor, then switch it to manual (the hand)
    and set the dial to 180°. 140° if theres no thermostatic mixing valve on the S120.
  • rfrozy
    rfrozy Member Posts: 7
    You guys are really awesome. I really appreciate the time and effort you put into your comments. Benny I'm pretty sure the system is set up as method 1. There are no room sensors. HVACNUT I will change it back to auto and we have an outdoor sensor so that's been on auto never touched that.

    If I keep the house at 65 for the day and I want it warmer am able to adjust the thermostat do so or does the thermostat just tell the buderus what the room temperature is? When I was trying to figure out the system I cranked the thermostats to 72 but I never got things hotter then MAYBE 68 OR 70 and that was pushing it.
  • rfrozy
    rfrozy Member Posts: 7
    Reread and saw the answer regarding the thermostat. My apologies. Correct me if I'm wrong. Just want to make sure I understand.

    Schedule is set on logmatic for day and night heat.

    Thermostats tell logmatic the temp and turns on zones when it's below the set temp on logmatic.

    Thermostat can override scheduled temp on logmatic but it's best to keep at a constant temp then to try and play catch up.

    The only thing I'm not understanding if this is the case if I crank it up at some point the rooms should hit the 72 correct?
  • BennyV
    BennyV Member Posts: 47
    The dial is a mechanical override for the upper limit. "AUT" is 230F, which is where it should stay. If for some reason the R2107 malfunctions and fires the boiler continuously with no zones calling, the mechanical limit will stop it from boiling over. Note that the boiling point of water is about 255F at 17psig where most heating systems stay. Crafty Germans, everything is redundant and over-engineered.

    The rocker switch on the right is an override only if the board fails and gives you no heat and hot water. You set the dial to 140F, and it turns on both the power to the zones and the indirect. You may not have full heat at colder temps, and if you don't have a thermostatic mixing valve, you DO NOT GO ABOVE 140F, as your hot water will be basically the same temp as the boiler. This is an emergency heat mode, not for normal use.

    It's mostly likely set up as outdoor reset (scenario 1). If it's set up for indoor reset, there can only be ONE indoor sensor, as you can't have two sensors controlling the same boiler, it's just impossible.

    Are you talking about the thermostat or the BFU room sensor? Like we discussed above, the thermostat doesn't tell the R2107 anything, the R2107 maintains it's heating curve and the DHW tank, and the thermostat controls the zone board, which controls either the pumps or a pump and zones valves that control the zones.

    Remember that the R2107 is designed for a German heating system, which uses manual mechanical zone valves with a pump that's always running, and responds to pressure in the system, so that water is always available. The radiators are plumbed in parallel, and each individual radiator is controlled by a mechanical TRV (thermostatic radiator valve) on the radiator itself. The R2107 is designed so that the TRVs can stay set high, and the R2107 manages the temperature and setbacks. The Germans set up their systems with such precision, and they have large, heavy, high-mass buildings, so the R2107 running only on outdoor reset can, in many cases, be set up precisely enough to manage indoor temperature without a direct feedback.

    Here in the US, that probably wouldn't work as precisely, so we need either the BFU room sensor in the main zone, or an outdoor reset curve set slightly hot with electrical thermostats in each zone to make the final adjustment to the temperature. Keep in mind that an R2107 can perform beautifully on an American zoned system, but you can mashing together two totally different paradigms of heating systems into one system that has to work together. Typical American systems keep the boiler at 160-180F all the time, and whenever a thermostat call comes in, the pump or zone valve for that zone is opened/turned on (zone boards for valves manage both the pump and the valves) so that hot boiler water surges through the radiators, often making them crackle and clank, heats everything up really fast, and then shuts off, leaving you to feel cold. An R2107 not only makes the boiler more efficient on it's own, but it makes you feel more comfortable, so you don't have to keep turning the heat up and cycling the system and using more oil because you were cold, and then you get hot and turn it down and so forth and so on.

    The US uses 70F indoor design temperature, which is generally too hot, but you have to account for elderly or sick people I guess, so that sounds like the curve is pretty well programmed, at least at whatever the current outdoor temps are, as the offset can change the shape of the curve as well to match the building.
  • BennyV
    BennyV Member Posts: 47
    I'm not trying to yell at you here, but I capitalized some stuff for emphasis, because it's really, really, really important. Re-read and understand the emphasized stuff, because if you can't wrap your head around it, the R2107 will never make sense to you. Once you understand how it works, it will make perfect sense, and you will realize that it's an elegant solution for controlling a high-temperature radiator/convector type of heating system with an indirect hot water tank (sometimes called a heater, DHW tank, DHW heater, indirect tank, etc).

    NO NO NO. Re-read what I posted above. The Thermostats tell the R2107 NOTHING. The R2107 maintains it's heating curve. The R2107's setbacks assume that the radiators are constantly circulating, i.e. the thermostats in an American system or the TRVs in a German system are never satisfied. So if your thermostat is set at 68F, and you have your heating curve set up perfectly for the system, you could set the day temp to 65F and night temp to 60F, and using the boiler water temperature, the R2107 would change the boiler temperature to make the indoor temperatures 65F and 60F, and the thermostat would never stop calling, as it would never get to 68F.

    The problem with that theory is that it doesn't really work in most American homes. Most American homes are lightweight, wood framed buildings that have air infiltration issues, so the heating load can jump way up when it's windy or cloudy out, so an outdoor reset curve based only on temperature isn't going to work accurately. If you use outdoor reset only on the R2107, you are just aiming to get it close, and then normally the hardest to heat zone's thermostat will call for heat 80-90% of the time in typical conditions, allowing for it go close to 100% of the time if it's really windy and cloudy out, and 50-60% of the time if it's bright and sunny with no wind.

    NO NO NO. The thermostats control the zone board, which controls the zone valves or pumps, depending on how the system is set up. Valves versus pumps are irrelevant to understanding the R2107's operation, but important to have set up properly to get enough flow through all the zones without using too much power, depending on how your system is plumbed up.

    The ONLY interaction between the R2107 and the zone board is that the zone board should be powered off of the R2107, I believe it's pin 63, but I could be wrong, check the manual, so that when the R2107 needs to run hot water, it can shut the heat off for a few minutes, take care of hot water, and go back to heating the house. Without this control, you could run out of hot water, but in milder weather, if the boiler is operating at, say, 110-136F, and it needs to go to 170F because someone is taking a bath, it would have to heat up the entire heating system to 170F, overheating it, and hitting the thermostat or TRV set points, shutting the whole system down for a while, and then causing the on-off cycling that it's designed to avoid in the first place. By running hot water only, and then switching back, a little bit of extra heat can make it's way into the heating system, but it's quickly absorbed by the mass of the heating system, and it's unlikely to hit the thermostat or TRV setpoint.

    NO. The thermostat DOES NOT AFFECT the heating curve of the R2107. The R2107 has no way of knowing if a thermostat is calling, and all the zone board knows is if it's calling or not, it's an on/off contact, not the temperature.

    Like I said above, the only way to use a programmable thermostat is to use it on zones OTHER THAN the hardest to heat zone, assuming that not all zones are perfectly balanced and installed like the Germans do. Let's call this upstairs. Since heat rises, and radiators are generally installed on a per square foot basis, the upstairs is USUALLY easier to heat. You could have either a set outdoor reset curve that is set up for the downstairs zone, or have the BFU room sensor downstairs controlling the reset curve, and a programmable thermostat controlling the upstairs. However, because you're still on a reset curve, you can't quickly recover the upstairs, and the savings would be negligible at best on a system with reset control, so I would only do this if you have, say, an office upstairs and you need it to be 64F during the day, but you can't sleep above 59F.

    The BFU room sensor is NOT a thermostat. It is in *indoor* reset control. If you have the BFU room sensor, you set the R2107 to favor the indoor reset control more than the outdoor reset curve (it still uses some algorithm to combine the two), so the boiler temp is mostly controlled on *indoor* temperature. Then, you use the BFU room sensor, which is set to a constant temperature, for your hardest to heat zone, and that zone's thermostat is a few degrees above the BFU room sensor setting. The BFU room sensor DOES digitally convey the room temperature to the R2107's computer board, but it is NOT a thermostat, it's really not much of anything other than a sensor and keypad that feeds signals back to the R2107. You can set it to day and night from the BFU room sensor's buttons to manage setbacks manually if you're up late or early or whatever. The BFU room sensor's zone's thermostat is still a simple on/off contact on the zone board. In that setup, the thermostat from the hardest to heat zone where the BFU room sensor will be calling all the time in colder weather, and most of the time in the shoulder season, as the BFU room sensor, which is just an extension of the R2107, is feeding that data into the R2107, and the R2107 controls boiler water temperature to control the room temperature more precisely.

    It gets a bit wonky in shoulder season, as the boiler can't operate below a finishing temperature of 130F, it can shut the pumps down when below 104F, and it will often get up to about 155F to run hot water, but then it would heat to the thermostat and shut the zone off for a bit to balance everything out and you're not really doing indoor reset anymore, but no harm no foul, you're still a ahead of an outdoor reset curve, and way ahead of old school aquastats where you're sending 180F water out into the system all the time when it's 50F outside and you just need a tiny bit of heat.

    The R2107 would destroy most other oil boilers, because it's based on protecting a Buderus boiler, which can operate at very low temperatures, thanks to Buderus's patented flexible cast iron. Sorry to sound like a sales pitch, it's not, but it's a different material than your average oil boiler. The R2107 allows the heating loop's temp to drop all the way almost to the room temperature if there is nearly no load on the building, but it then shuts the heat off and fires the burner until the boiler reaches 104F, and continues firing until the whole thing has reached 130F, in order to avoid condensation, as the laws of physics still apply to German made products. Without the R2107, you can't go below 130F for normal operation of a Buderus boiler at all, since you don't have the protection algorithm to finish the cycle off at 130F. Most other oil boilers don't like to go much below 140F at all, since they aren't designed to run at lower temperatures like Buderus.

    NO. If the reset curve and everything else in the system is absolutely perfect, and the R2107 is set for a room temp of 70F, then it should get to 70F and not be able to go any higher, as the boiler water is only hot enough to get it to 70F. American houses and systems are rarely this precise, but if you can get it that close, bravo! Personally, I'd get the BFU room sensor, put it in the coldest/hardest to heat zone, set that zone's thermostat 3-5 degrees above the BFU room sensor, and let that modulate the boiler temperature, and set the other thermostats where I want them, and just leave the system to do it's thing instead of fiddling with thermostats constantly.
  • BennyV
    BennyV Member Posts: 47
    Just to add one more though to clarify, if you're using day/night setbacks on the R2107 and controlling it with the BFU room sensor, you are controlling the boiler's water temperature, and thus the temperature of the entire system, and the R2107 knows to fire up the boiler hotter to recover in the morning. That's fine, as long as you manage it with the R2107.

    Traditional thermostats assume the boiler is always at 180F, so they cycle the zone on and off entirely to run setbacks, assuming that there is an endless supply of 180F water to recover the zone again in the morning. This is why a programmable thermostat doesn't work well, or really at all, with the R2107. A NEST will either force you to set the reset curve too high and lose part of the benefit of the R2107, or it just won't recover for hours and hours, and you'll be cold.

    If you absolutely need setback in a secondary (easier to heat or upstairs) zone, it would be wise to set the recovery to happen at the same time as the main (harder to heat or downstairs) zone is set to recover via the R2107 and BFU room sensor, as the boiler will heat the water up hotter to do the main zone recovery, as controlled by the R2107 so the secondary zone's thermostat will have a little bit easier time recovering, as opposed to just relying on the fact that it's a little easier to heat the upstairs zone at any given boiler water temperature than the downstairs zone, which could take many hours to recover.

    I would personally recommend setting any setbacks through the primary zone on the R2107 with a BFU room sensor, and then leaving the other zones at a constant temperature with their own thermostats. If the zones are close to perfectly balanced/matched, then the secondary zones will call all night and "droop" a bit, and recover with the primary zone in the morning, and then finish the zone call after they have fully recovered, and go back to whatever ratio of on/off they had. A well designed and balanced system would push the secondary zones closer to 90/10 or even higher, a poorly designed and balanced system might be more like 50/50 or 75/25. If you keep the secondary zones much cooler, then you'll go more towards 50/50 than 90/10.

    Lastly, the hot water shutoff feature is idiotic. I've done the calculations out, and even with an older indirect tank, you might save a gallon or two of oil per year. Set it for 24 hour operation, and don't look back. It must be a culturally German thing from a bygone era when keeping things hot actually took a lot of energy. With modern super-insulated indirect tanks, just set it to 24 hours and forget about it. Unless it's a second home and you're away for extended periods of time often, there really is no purpose in shutting it off when you're not there either. It just doesn't use much of anything to keep it hot and ready to go.
  • GW
    GW Member Posts: 4,542
    Wow I’ve never seen so much typed out on the 2107. You heating dudes are the jam, trying to explain this is very difficult. It’s easy for us because we use this language and logic daily. Telling someone it’s easy has it’s pitfalls though. Explaining in person is a bit better. We can’t see the persons ability to take in the tech info

    Yes, 63 is the correct terminal. I always remembered a little rhyme, ZC to 63. Drop the jumper Zr to Zc

    I am an advocate of the BFU. I wish to install the BFU on the more/most dominant or most warm zone. Note- you must tell the 2107 you installed it!

    Potential problem——-you install a BFU on the main house zone which has honking big rads, and your dumb stats operate a more modern baseboard zone. Oooops you have a problem. There are ways to trick the 2107 but that’s getting into crazy talk

    BFU——don’t forget to adjust the Comp setting, I jack it to 18 every time.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • SuperTech
    SuperTech Member Posts: 1,792
    edited November 2018
    @BennyV and @rfrozy thank you both very much for the knowledge that you passed along on this thread. As I service technician I might see 2-3 Logamatic 2107 controls a year. I have a basic understanding of how it works but I never completely understood how it works until now. This is exactly why I visit this site daily during heating season.

    I worked on one today, boiler installation was beautiful. The only problem was it was piped for several zones of hydro air. It had one zone of radiant to heat the slab in an unfinished basement. I told him he made a mistake when had the first co units installed.

    And the manual for the Logamatic is terrible for explaining operation. Buderus should hire Dan Holohan to rewrite it for Americans.
  • D107
    D107 Member Posts: 1,800
    @BennyV HO here with same setup. We switched from t-stat control in both zones to BFU indoor sensor on Main zone and left t-stat on zone 2. One of your posts here recommends keeping t-stats on both zones of a two zone system and adding a BFU indoor sensor to the main zone--or hardest to heat. I had heard that was possible but am wondering how the wiring would be to have indoor sensor and t-stat on one zone. When we did ours we ended up with constant circulation, and the main zone circ no longer was activated by the t-stat taco relay but by boiler water temperature curve as facilitated by the indoor sensor. Wiring change was fairly simple, but with your recommended set up you're saying you end up with main zone running both off the t-stat/relay as a high limit AND indoor sensor for water temp? Not sure if any Buderus manual has the wiring diagram for that combination.

    Also I think some experimenting has to be done to figure out where the best place to locate the thermostat is--not near a TV, sun exposure, oven heat, radiator, drafty windows, etc.

    Also, yes the original user manual was not too clear; service manual was a little better. Then they came out with an Applications Manual--better still. I have copied and pasted much of the advice I have received from Buderus techs and the original Buderus online chat room which was so helpful since so much of what the 2107 can do is undocumented in the manuals.
  • BennyV
    BennyV Member Posts: 47
    @GW - Yes, anyone who reads that wall of text should get a prize haha. It's hard for a lot of people to wrap their heads around, as you first have to understand how the Germans use heating systems, and then how Americans use them.

    By most warm, do you mean the one the occupants keep the warmest? If you install it in the zone that tends to run warmest, wouldn't the other zones not have enough temperature to heat to the setpoint?

    Yes, that's true. You could end up with a scenario where the fin-tube has a harder time in mild weather, and the CI has a harder time in colder weather, so neither location would work entirely for the BFU. It would depend on the house, construction, and alternate heating sources available.

    @SuperTech The R2107 is a challenge with hydro air. It can work, but you have to find a way to shut down the air handlers during a DHW call, or else they just orbit cold air around. Buderus advertises the R2107 as working with hydro air, but I think that's a bit of a stretch. It's a weird control to use with hydro air. The Germans don't have hydro air, as they don't really do A/C in most places, and are really into hydronics.

    @David107 Yes. The BFU room sensor has it's own terminals, and the zone board is run off of pin 63, so the R2107 can shut it down entirely when you hit your seasonal shutdown temperature, which, IIRC, is an OAT of 16C or 17C per German heating code, so on the German units that's somehow limited or locked, but on the American ones you can do whatever with it.

    With both a BFU room sensor and a thermostat, you just have to keep the thermostat set above the BFU room sensor's highest settings, and it's effectively the same thing as having the circulator set up for constant circulation, except that the thermostat will trip in the shoulder season if the loads are really, really low, and the BFU room sensor will lower the boiler setpoint anyway, since the room would be over the BFU's setting.

    The problem is, what is in the Bosch manual, what is posted by users online, and what the Bosch rep says about how the heating curve is calculated are three different things. If you have the BFU room sensor, it doesn't matter that much, but for a system with different types of radiators and convectors, hydro air, or where you want to set an ODR curve without the BFU room sensor for whatever reason, good luck figuring out where your curve will go based on the offset and the manual.

    They really should develop a more versatile control for the US market that can take input from the TT connection on a zone board and handle buffer tanks, hydro air, reverse indirects, and other types of edge-case installations better, as well as report back to the dealer via Wi-Fi like some gas boilers are doing now. If the dealer could reset a customer's heating curve from their couch, they might be more likely to try and push the limit on reset curves and whatnot versus playing it safe.

    Bosch also should have a calculator or easier way of setting the heating curve that makes more sense to Americans. As far as I can tell, the "Reference Temperature" of 14F/-10C is the design temperature in Western Germany, so their radiation is designed for 90C water at -10C OAT, versus US systems that are designed for 180F at 0F or lower OAT, as oil boilers don't really exist in the US too much south of Long Island or New Jersey, which have a design temp of around 0-5F.

    Lastly, there should be more options for how the control operates, i.e. DHW priority which is 100% necessary on a system with honkin CI rads is a detriment on a hydro air system, options to work with a buffer tank or reverse indirect, or the ability to have a TT line fire it up to full temperature for an application like a unit heater in a garage or basement that's only used occasionally to heat up quickly, and then when the unit heater is not calling, return to it's normally scheduled programming. I sense a cultural gap where the Germans are like "This is how you heat!", and Americans are like "But Freedom, we invented all kinds of whacky stuff we can plumb up to a boiler. Here in America, we can have a reverse indirect, a buffer tank, micro-zoned radiant, fin-tube mixed with CI rads, a hydro air handler, snow melt, and a pool heater because why not?".

    That being said, it's a neat control on the right type of system, and short of micro-zoned outdoor reset radiant, it will be more comfortable than any other heating system.
  • SuperTech
    SuperTech Member Posts: 1,792
    There's definitely a cultural gap. I think the Germans would not approve of my two pipe reverse return Venturi tee system for cast iron baseboards. They certainly would frown upon my pin type single pass boiler.
    Great thread, I wasn't looking for this information but I'm sure glad I found it.
  • Noel
    Noel Member Posts: 177
    Great post, I'm glad I found it. This sheet is handy to have at start-up.
  • rfrozy
    rfrozy Member Posts: 7
    First of all thank you Benny for all the extreme amount of time and effort you put into your responses.

    I didn't get to process it all yet. I plan to study it in the AM. I came on to say you guys helped me big time in getting things under control and figured out. I shut those damn thermostats off of everything but the very basic settings. I have the 2107 set to automatic and the day set to 65 and night to 63 and things have been perfect during the day since I did that. I still have to tweak the night a bit. It's an inferno around 2AM then cold by 530 when we get up. I think there's some old scheduling still in there that I might have missed.

    Thanks for yelling at me though. You were able to break it down in a way that I could understand it.i was so used to the forced air and this system is literally foreign. Regardless most kinks seemed to be worked out.

    I still have a couple bedrooms that aren't getting warm. I gotta check under the drop ceilings and see if there are some valves. Otherwise I'm flying the tech in from Germany after Christmas.

    Thank you again for the help.
  • BennyV
    BennyV Member Posts: 47
    Glad it helped! You might want to write down your settings and factory reset and reprogram, or else go through the schedules step by step if you're not sure what's in there.

    Scorched air is totally different, as there is a negligible amount of mass in the system. Hot water is a medium- to high-mass system, so the dynamics are very different.

    Are you getting circulation at all through those rooms? Are they on another zone somewhere that's not working?
  • D107
    D107 Member Posts: 1,800
    edited December 2018
    @BennyV yes thanks so much for your information.

    You said. "...With both a BFU room sensor and a thermostat, you just have to keep the thermostat set above the BFU room sensor's highest settings, and it's effectively the same thing as having the circulator set up for constant circulation...."

    The other method I've seen used --if no BFU but only T-stat control, is to keep the t-stat setting BELOW the 2107 setting so that the water temps will always be a little higher than required so as to be able to handle any requirement. Buderus has recommended this. But then constant circulation will not be automatic, you'd have to set it up that way. Have you used this method?
  • BennyV
    BennyV Member Posts: 47
    @ David107 That's correct, you can set the reset curve slightly above what the building needs and the thermostats will get you to where you want to be. Constant circ with the BFU room sensor is preferable, as it gets the curve perfectly dialed in, and it can respond to wind/solar gain, which can be quite significant in some buildings.