T and TV (thermostat control) terminals on L8148E are jumpered together

MaMa

I'm a homeowner who has purchased a house with an installed Buderus G124X boiler (no DHW, just space heating), and have been trying to puzzle out how it works.  One thing that had me stumped was that there is no visible wiring between the boiler and any other components of the system (pumps, thermostats), and now I think I understand how it can work that way: there is a jumper between the T and TV terminals on the aquastat L81418E.  If I understand various manuals correctly, doing this means that the boiler (when power is applied to circuit) will always maintain the temperature of the water in it at the setting on the aquastat dial (180 degrees), and if it drops sufficiently below 180 (whatever the differential is), it will fire again to reheat it to 180 degrees ... all of this happening whether the thermostats actually are calling for heat or not?



The system has three zones with individual pumps on each zone, and a thermostats connected to & controlling each of the of three pumps, rather than the aquastat.  I think I see how this "controls" the boiler: when there is no call for heat, none of the pumps run, and without water flowing in the system the temperature in the boiler well drops very slowly, ergo it runs infrequently.  But if one or more zones do call for heat, the pump(s) are started, and the circulating water will more quickly cause a drop in temperature in the boiler, causing it to kick in more frequently/longer, because lower temperature return water keeps running in.  Does that make sense?



Then my next question is, is this desirable (or rather, is it undesirable)?  It seems kinda inefficient, most particularly in the summer months & extended periods of warm weather, if you leave power on to the boiler.  I assume the T and TV terminals are there for a good reason, not merely to be shorted by a jumper so they essentially do nothing.  Based upon my self education, what this way of installation is saving is the need for a switching relay like the Taco SR503?  Maybe the contractor/previous owner (the boiler was installed maybe 7 years ago) was trying to save money by omitting that?



My final question is -- hope I'm not getting to ahead of myself, without having the answers to my previous questions -- if I want to add the benefit of ODR to this system, via the logamatic 2107, is this "hacky" (if my instincts are right here) installation going to get in my way, am I going to need to purchase additional components to get the benefits of the logamatic (switching relay, room sensor, or whatever)?  Or perhaps, conversely, adding the logamatic will somehow give me better control of the boiler WITHOUT having to add additional relays, etc ... the combination of lower boiler temperatures and WWSD abilities can make the issue moot?  That is my instinct here, however the 2107 application manual does not appear have a scenario remotely like this, so I'm not sure how to proceed.



I'd appreciate any validation of my interpretations/advice



Mark

lchmb

dont take

this the wrong way. But sometimes things are best left to a pro. If everything is wired properly your system will go cold unless there is a call from a t-stat. T-T is the low voltage signal to your boiler to start which will come from your circulator control box. If your boiler is wired to run at high temp then you need someone to come in and correct this issue. Simple test, it should have sat cold all summer. If it did not something is wrong.

If you wish to have a logamatic installed, do so through a trained technician. That way he can check the system over for proper setup and function to include testing all safeties.

MaMa

.

It sat cold in the summer because the power was cut to the boiler, via a switchbox that the previous homeowner turned off in the spring, as he personally explained to me he did every year.  After I turned the switch was turned on a few weeks ago, the gauge on the boiler maintained temperature of around 150 degrees, even when we had unseasonably warm temperatures outside up in the 80s, going no lower than the 60s overnight for many days running, and the boiler gauge continued to show around 160 in those conditions even a couple days after I set all the thermostats to their lowest setting (in the low 50s, i.e. below what the lowest temperature outside was)



Why (how) do you think the the boiler could ever go cold with power applied & without any thermostats or any other controls connected to it, but rather a jumper across the thermostat hookup wires of the aquastat?  How, electrically speaking, could the boiler have any awareness of whether there is a call for heat by the thermostats, if the the termostats are only wired into the ower supllies to the pumps?  I confess I have lost you here.  I'm not an HVAC professional, no, but I am an engineer & do understand electrical control principles.

lchmb

That's

the problem. The jumper across T-T is the issue. Your control box (if you have one) for your circulator's should have an end switch that will notify your boiler to come on. The way they have it wired now is wrong and will cost you a lot of fuel in the fall and spring. I would recommend you get someone in to correct that and would suggest either the logomatic control or a tekmar system. Both will work to lower your fuel usage.

Since you do electrical, look at the wiring for the Taco SR503 control. It has an end switch which would be wired to T-T on your boiler aquastat. T-stat calls, circulator is energized, signal is sent, boiler comes on.

no call..no heat...no fuel burnt...

btw, if your controls are the 845 single zone control I would suggest the purchase of a taco (or similar) control. Much easier to wire and you have a signal that tell's you what's doing what...

MaMa

Thinking a logamatic 2107 alone will eliminate most of the negatives?

Thank you for the reply, lchmb; I'd pretty much already concluded it was a problem, I was looking here for some validation of my conclusion.  Wanted to make sure this was some standard but "secret" trick installers used that I was not appreciating the "beauty" of.  As I said, I believe I understand how it "controls" the firing of the boiler, but i see no "beauty" in it.



I've spent the last hour exploring the idea I expressed in my last paragraph: "adding a logamatic 2107 may give me better control of the boiler WITHOUT having to add additional relays, etc ... the combination of lower boiler temperatures and WWSD abilities can make the issue moot?"  I've just about convinced myself now this may be true, if I wire the T-TV terminals of the aquastat to the 10-11 terminals of the 2107 "Brenner" connections (along with rewiring the line voltage from L1-L2 to terminals 4-12), and set the WWSD temp appropriately.  Then the 2107 WWSD will shut off the boiler completely (let it "go cold" as you say) in the summer & in the warmest interludes of the shoulder season, and the 2107 ODR will greatly minimize wastage in the periods of outdoor temps slightly cooler than WWSD because it will make the boiler heat to a lower temperature (and the system will run for longer periods, and the heat loss from the boiler when the water isn't circulating will be a lot slower when there is a smaller temp differential with the basement ambient temperature).  As the Buderus manual for the 2107 states, it is not a cold start control anyway -- it looks like even if I had had a thermostat hooked up the aquastat before, I'd need to disconnect it from everything  but the pumps/switching relay once I put the 2107 in.  The only thing weird here is I just wouldn't connect anything to the 2107's HK-I block (terminals 61 & 63 (I hope the 2107 will still function if nothing is connected to the HK-I?)  I've started to realize I think a relay like the sr503 is only necessary if you have one system pump + valves in each zone.  If I have the 2107, no valves to control, a pump on each zone, and each pump is already wired to be controlled by a thermostat, then the only benefit I lose by not having something like the sr503 is the warm weather "pump exercising" feature of the 2107?  (I don't see the need for priority at all) If that is all, not sure the cost and hassle of installing a switching relay as well as the 2107 is worth it?

lchmb

2107

 is an awsome control. I have a feeling you'll be happy with the system once installed. I recommended the circ control in lieu of using the control, to at least keep the boiler off until there is a call for heat, specially in the summer with now WWSD...I just didnt explain it to well..:)

MaMa

Well, the deed is done

Well, I got the Logamatic installed last night, and amazingly I turned it on & it all worked (or at least seems to, so far).  Whew woulda been hell to pay with wife if it hadn't, and I was running out of time, temperature outside had gotten into low 40s overnight, and low 60s inside.



I watched it for a while, and with mostly default settings to start & with the ODR temperature reading 41 degrees F, the 2107 was kicking in the boiler when the water dropped to 113 degrees F, and cutting it off whine it hit 138-140.  At those settings, based upon a check 5 hours later, it looked like the house was getting heated about a degree per hour.  I take that slow warmup as a sign that things are probably about right, since the whole point here is to running longer at lower temperatures, which is going to mean less rapid heating.  I'm currently running it in "day" mode (not auto) because it was late when I finished & I needed to catch-up on the indoor temperature, and how the setback can work without an internal sensor is still baffling to me ... and as noted earlier, the #1, #2, and #3 immediate objectives here were satisfying the spousal unit we would have heat again



I can see there is significant further learning I have to do here, to configure the 2107 optimally, and I'm guessing that will be ongoing through at least one heating season.  I also did some more reading, and I think I now understand that the  configuration I have -- thermostat controls wired to control pumps but not the furnace -- is maybe not that unusual, it is called "Stand Alone Water Flow Control with Partial Outdoor Reset" in the Tekmar literature.  I'll likely wait some time here to evaluate how well this works for me & learning what I can & can't do with the 2107, but I am already starting to consider (at least enough to put into context the limitations of the current setup) indoor sensors &  central zone control on the pumps.  Two more electrical/wiring thigns that I feel I could take on personally.  Don't want to touch anything involving the actual plumbing, eg mixing pumps!



Thanks again for your feedback lchmb.

lchmb

no problem

btw, studies have shown any more than a 6 degree setback is a waste of time. When running with ODR I actually recommend to people to turn the bedroom down (most people like it cooler to sleep) and leave the house alone or just drop it a couple degree's...btw, indoor sensor's with the logamatic just make it that much better. I would recommend picking up one spair sensor just in case one goes bad...

MaMa

setback

I like it a little cooler in the bedroom at night too -- and the side benefit would be that the pipe expansion noise (diminished but still there) would lessen long enough to at least get to sleep.  So I am thinking about a kind of compromise, putting a normal set back thermostat there in bedroom zones & programming it to go down, but leave rest of house zones with no setback.  I've read elsewhere as well that the SETBACK on the 2107 leads to slow recovery, so minimize or avoid using it, but ... I guess that does not make sense to me if you have normal thermostats and you do not turn them down (as I am thinking of doing in other two zones, on lower (cooler) levels of house).  In that case, what recovery would there be, the temperature would never change?



I think I am starting to understand better SETBACK vs RMSETBACK (setback with remote/room sensor).  I think Buderus made it a lot more confusing than it needed to be.  What's confusing is that the SETBACK mode is designed to be used only when you DON'T have room sensors (ergo your control doesn't know what the internal temperature is), but ... the settings you make to control it are in terms of indoor room temperature, the thing the control can't measure!  Huh?  I think I'm starting to comprehend that what it really is is not setback at all -- or rather, nit isn't alone, only in conjunction with matching it to settings on a thermostat in the zone(s).  In other words, the DAY and NIGHT settings are not setting back the temperature at all itself, it's only for "informing" the 2107 what target temperatures that you will be requesting of it, so it can intelligently calculate heat replacement amount/heating curve (and therefor optimal boiler temp).  It *kinda* says that in the application manual, but I thik it could have been made a LOT clearer.



p.s. I'm still going through sticker shock at the price of the BFU room sensor.  $130!?!  Yikes!

Jean-David Beyer

I like my bedroom cooler at night too.

My main heating zone, that includes my bedroom, is a radiant slab. There are 5 loops in the slab, one under each room. Each has a ball valve (not ideal) controlling the flow. So I reduce the flow to the bedroom. The largest two rooms and the bathroom all run at maximum flow. What this would mean is that the bedroom would be cool in the daytime too, and this is the case. For me, this is not a problem as I do not use the bedroom much in the daytime, and I just leave its door open during the day.



As far as expansion noise, I do not get any with the slab. I have another zone with baseboard. I used to get lots of expansion noise with that with my old boiler: no outdoor reset. My new boiler does have outdoor reset and I have the reset curve for that zone set to be very close to the heat loss, so the circulator runs most of the time. The water temperature changes only slowly, so there is much less expansion (and contraction) noise than before. I imagine there would be even less, but my boiler will not modulate down far enough in warm weather if that zone (very small heat load) is the only one calling for heat.

MaMa

Cooler bedroom

The conundrum I have is if I want (prefer) it cooler at night I have to do setback, but if I eventually tune the logamatic tightly enough so that I'm close to the ideal of just replacing heat loss, if I do any kind of setback then I'm going to have very slow recovery UNLESS (it appears) I get the BFU room sensor and take advantage of this "boost" mode for recovery that it has.  But, I don't think I have any zones that would work well with the logamatic BFU the room sensor:



1. The upper zone (bedrooms) has perimeter baseboard in each room, and thermostat located in central hallway, where there is no baseboard.  Typically 3-4 of the 5 rooms off the hallway have doors closed at night.  So the whole feedback loop (the point of the room sensor) would seem to be unreliable, with thermostat so far away from heating & closed doors between it & most baseboards during recovery period, it will look to sensor/logamatic like recovery is very slow, when in fact the rooms will probably be heating up, just that the heat will not get into the hallway because many of the door are closed.



2. Zone 2 is a large open floor plan area, with a fireplace in the middle, a wall of large south facing windows, & current thermostat wired to a location right across from fireplace.  Seems like a bad idea for a room sensor that will control heating curve for whole house!



3. Zone 3 is another level that is dominated by one large area with a second fireplace & also the current location of the thermostat.



It seems to me what would be better for my situation is to not use the BFU room sensor (which I have read that even Buderus reps do not recommend much when there are multiple zones, even without the special circumstances of mine) & just go with normal thermostats, maybe with some kind of intellignet pump zone control to try to coordinate heating & minimze cycling a little.  I think it would work, and I could have setback PLUS control well tuned for heat loss during normal hours, if I could only get the Logamatic to run in "boost" mode (higher temps) during setback recovery even though there is no room sensor connected.  But it does not seem like this is possible, inexplicably, boost mode only will work if there is a room sensor somewhere?

MaMa

p.s. logamatic "pump logic" setting and circulation control

As I am (very) slowly gathering understanding how this system & control works, I think I am coming back to my concern about the pumps only being controlled by the thermostats again (nothing currently wired to the terminal 61-63 space heating pump control).  Am I correct that in this situation I could be defeating the point of the 104 degree setting on the pump logic setting to protect the boiler, that I could have a scenario where the water temp has dropped below 104, but because the pumps are only controlled by the stats, water can be circulating?  Or is this realistically only possible only if WWSD is in effect, otherwise the logamatic will ALWAYS fire the burners before it gets below 104?



God this stuff can be complicated!



Maybe its better just to be safe rather than sorry & get a pump switching control and let the logamatic have the control it expects.  I am looking at the Taco SR503 and SR504, but the idea of what tekmar calls "integrated zone control" is intriguing, trying to get a pump switch control that maybe does minimal coordination of the heat calls from each zone. Say delay the startup from first heat call from cold state for X minutes, and/or keep running a zone whose heat call has been satisfied an extra Y minutes if there is another zone still unsatisfied.  Does that makes any sense, is there such a control?  Accordign to the Tekmar essays, zone control coordination has a number of advantages, should increase fuel cost efficiency, but it looks like their products that implement it (tn2 etc?) are not compatible with my situation with logamatic and pumps on each zone (not valves?)

lchmb

opinion

I think if you give the 2107 control through a taco sr500 control you will get what your looking for. Adding a tekmar to a 2107 seems like over kill to me.

MaMa

thanks again for reply

Sorry if I wasn't clear lhmcb --  I actually only mentioned tekmar in reference to the PDFs I am reading in their "education library;"I didn't say I was looking to install any specific tekmar products.  As I said I'm already looking at the Tacos, specifically sr503 and sr504.  Tekmar came up only to frame the question that came to me after reading their PDFs: are there any pump switching boxes that coordinate the heat calls between thermostats?  The Taco sr50x units (correct me if I'm wrong) don't coordinate transmitting to the logamatic the heating calls from the multiple zones at all, they just pass them on as they come & go (i.e. they are truly merely a relay)