Buderus system out of control? Any Buderus experts out there?


Old 11-06-10, 04:48 PM
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Exclamation Buderus system out of control? Any Buderus experts out there?

My father in law has a Buderus G115 boiler that's about three years old. He had no heat about a week ago, and the heating guy that came out (who knows about as much about Buderus systems as me) determined that the outdoor temp sensor was shot since it was reporting the outdoor temp to be 104 degrees. Being October in upper NYS, this seemed logical...

Background - my father in law is 86, and not into new technology. Although Buderus has lots of slick features for programming summer cutoff, vacation settings, and night time set back, he's an old fashioned kind of guy that just wants to turn the dial and get heat, and not have to worry about whether he's overriding or combatting a preset program to get heat. He uses the system in manual mode.

After replacing the sensor, everything seemed to be working okay, however the first night the temp in the house kept climbing gradually throughout the night, to the point that it was 91 degrees in the morning - inside. Still in upstate NY....in October... My wife called me to come over, since the boiler's Logamatic control panel was reporting a "DHW PROD ERR". I told them at that time to shut off the boiler until I got there. I'm an Architect, and have very limited knowledge of Buderus systems, but I visited the next day to see that the boiler temperature dial on the Logamatic controller was set to 140 degrees, instead of AUT (auto) on the dial, which is above 190 degrees. The Logamatic control manual indicated this is where it should be. It didn't take an architect to read that one.

I turned power back on to the boiler - no error message shown any more. Still 85 in the house. We warmed up the neighborhood by opening doors, and I set the remote sensor in the dining room at 68 degrees. The system fired when the room temp (as reported on the Logamatic display) reported 64 degrees. This I think was because while the room temp was dropping below set point, the boiler was already engaged making hot water for the domestic circuit. DHW is a priority zone I believe - someone can correct me. As soon as the DWH was satisfied, the boiler shut down and refired a few seconds later for heating circuit 1 (the house only has one circuit.) When the room temp reached 68 degrees, it cut out, as expected. What we didn't expect, was that the room temperature would continue to gradually rise again, until it reached about 75 degrees.

We were doing some heavy fall cleaning, and using many buckets of hot water, taking showers, etc., so the boiler was firing more than once for the DHW loop. I don't believe it fired at all for heating hot water, however all of the radiators in the house remained warm to the touch throughout the afternoon. After dinner I set the remote sensor down to about 64 degrees, and the room temperature remained at about 75 degrees throughout the night. This doesn't seem right to me for a boiler system that professes control capability to within half of a degree.

We've been told more than once by the mechanic that came out (remember, he had to read the owner's manual to understand the boiler, and knows nothing about Buderus) that the heating loop circulating pump is supposed to be running 24/7/365, but that it modulates down when there's no heating demand. This seems logical on a basic level, but illogical also. I predicted to the family that with everyone taking showers, filling buckets with hot water, etc., that if that pump does run all the time, there is residual heat in the boiler from it firing for domestic hot water that warm the water in the heating loop, and heat up the house even though it's not wanted. I appeared to be right. Curiously, when the boiler was firing throughout the afternoon, I checked both the DHW and heating loop circulating pumps for noise, using a socket wrench extension as my "glass on the wall". The DHW pump could CLEARLY be heard when it was operating - it was unmistakable when it was running vs. not running. The heating loop pump NEVER seemed to be on, even when the Logamatic control panel indicated it was on. It was more like "I can't tell if that hum is from the pump, or something vibrating through the pipe from the boiler..." Frankly, I don't think it was running right.

My questions for the experts here are:

In a Buderus low temp boiler system, is the heating circulator pump supposed to run continuously?

From my description here, does it sound like the heating circ pump has failed, allowing convection to circulate the water through the system uncontrolled?

Did I do the right thing setting the Logamatic dial on AUT?
Because of the DHW PROD ERR message, is there still something that a repairman would have to come fix?
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Old 11-06-10, 05:41 PM
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Ideally the circulator would run all the time. The boiler isn't set up to just run the circulator continuously. There needs to be a call for heat from the thermostat to have the boiler running etc. If the boiler was perfectly sized and all the other information perfectly calculated, it could run the system constantly using the perfect water temp. That's not an easy thing to do. There are many other variables that will throw things off. You can get very long run times though, but something is up with your system for sure.

Unfortunately, I don't have answers for you, but some others with more knowledge will be by to help. I can offer a tip to see if your circulators are on or not. You can get a couple 120V LED lamps from radioshack and tie them in with the wiring at the pump. You can also check for voltage with a meter.
Old 11-06-10, 05:45 PM
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The manual I'm looking at is here:

Page 61 has the dhw prod err description. Check that and follow the troubleshooting steps.

Looks like you can also do a full reset of the control to restore factory settings. See page 55.

In general, when the control is operating properly, the heating zone circulator should run as long as the room thermostat is calling for heat. The boiler will fire intermittently to heat up the water. If the thermostat is not calling for heat, then the heating zone circ should not run.

What make/model of room thermostat? Is this an AM10?
Old 11-06-10, 06:18 PM
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I should have mentioned that after replacing the outdoor temp sensor the heating mechanic did do a factory reset on the unit.

The sensor is not an AM10 - can't find a picture of it, but it looks like it would be the most basic type - just a knob to set the desired temp, with pushbuttons for night time, day time, and automatic controls...each with an LED indicator.

I would think that the circulator should not be running if there's no call for heat...but I wasn't sure about these modulated low temp systems...in my layman's knowledge, it would seem that in ANY system, if you aren't calling for heat, the pump should be off.

The heating circ pump casing is ALWAYS too hot to touch - vs the domestic circ pump which is only "very warm" when not running....
Old 11-06-10, 06:33 PM
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Was the tech that came out from the installing contractor?

Obviously it would be in everyone's best interest to NOT have him back again. You might want to start with the telephone now, and find someone who will assure you that they actually know what they are doing. I would think this should be the installing contractor, but ... well... maybe they don't know nuthin' neither!

Understand though that I'm not saying they should have the entire troubleshooting guide committed to memory, but they should at least have a working knowledge of the system...
Old 11-06-10, 06:38 PM
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When there is a call for heat, the circulator should run. When there's no call for heat, it should not.

What make and model is the room thermostat? Are you sure it is working properly?

From your description, it sounds possible that the thermostat is generating a continuous call for heat. In which case, the circulator will run all the time. And if DHW priority is off, then it will be pumping very hot water through both the indirect and the heating zone.

The circulators tend to be hot.

Is the 2107 set for DHW priority?
Old 11-06-10, 08:12 PM
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Followup 2 to Buderus out of control

Unfortunately the installing contractor closed up shop and took a job as a facilities guy at the airport.

The boiler is set for DHW priority.

I can't find a model number on the remote room sensor, but it appears to be the basic one for the 2107 Logamatic. There's no marking on it suggesting a model number... There's a mercury indoor/outdoor thermometer in the dining room as well, which is indicating maybe a 1-2 degree difference to the room sensor that reports to the Logamatic control panel on the boiler. Again, when the sensor was set to 68, and it reported that the room temp dropped to 64, the boiler fired. When room temp hit 68, it shut off. Since then, the house has been a consistent 75, with the room sensor dial set all the way down to the coolest temp. Logamatic says that that's 64. The LCD display at the boiler does show the Zone 1 pump as active most of the time - even though there's no heating demand... When DHW goes active, the zone 1 pump indicator disappears. I assume at this point that the heating zone 1 pump shuts off, but I can't tell for sure.
Old 11-06-10, 08:39 PM
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room sensor

It's a BFU remote sensor designed for use with constant circulating system.....did find that much...
Old 01-07-11, 08:41 AM
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Buderus acting up again....

It's been some time since my last post about the Buderus boiler running out of control and providing too much heat to my father-in-law's house. We never did solve it - the installing contractor went out of business, and the second "expert" could not solve it after spending two phone calls with Buderus to figure out how it's supposed to work.

We "solved" it for the interim by lowering the wall sensor's dial to 61 degrees, at which set point the house is maintained at a toasty 73-75 degrees. The outdoor temp sensor appears to report the outdoor temp correctly. The wall sensor appears to function correctly also. We have it set on MANUAL operation instead of auto, so that the night setbacks and other things don't override where we have the wall sensor set.

This AM - without any adjustment to the wall sensor - he woke up to the house at 85+ degrees. The radiators don't have any valves on them, so the pump is the only variable in the amount of flow, and it seems to be running way to fast. I'm an architect, not a mechanical engineer, so I need help diagnosing what other causes there could be, and how to determine which cause is the likely culprit... Could the Logamatic be telling the pump to run too fast? Could the pump just be shot? The whole setup is only about two years old...

Any ideas?

I'd like to go visit tomorrow with some encouraging news or ideas...
Old 01-07-11, 12:27 PM
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From what I read in the manual there is frost protection that kicks the circs on at a preset of 41F. Possible this needs to be changed.

If you have two circs there should be some type of flow control so when one circ runs the heat will not bleed over into the other zone. this could be faulty.

The remote control, if activated, disables the AUT, Day and Night modes are disabled at the key board on the boiler. And there is something about floor heating and a 6 degree F curve. Hence your 68F t stat and 74F room temp. You possible need to change the room compensator off.

The cicr runs constant on night setback with a room sensor. Default is out door. You may want to do away with the room sensor, but not sure. You would want the system to operate as intended but you may get rid of all the crap and operate with simple ON/OFF t stat.

There is a recirc-pump run time also for DHW that ensures constant HW. Possibly this is set to run and a flow control is bad bleeding heat over to the house zone.

There is a relay test where you could check all is functioning.

Basically if the unit was reset then some of the default values may need to be changed. These are things I would be looking at and as you scroll through some of the functions read and re-read you will get a better understanding of the system.

Times like this is when I say you can keep these types of boilers. They can do everthing but make coffee for you. LOL

Ill stick with my 30 yr old boiler. Still ticking.

Good luck and let us know.

Mike NJ

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