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Buderus G115 system not behaving...

jthompvt Member Posts: 1
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, or shut down after demand is met?

Could the BFU room sensor be bad, or could the boiler still be set too hot?

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?


  • meplumber
    meplumber Member Posts: 678
    Buderus Problems

    Ok.  Let's take one issue at a time.

    His assessment of the OSA sensor being bad was probably correct.  He should have taken an ohms reading to make sure.

    The other problems that you describe are more likely heat migrating.  As to your question of the circulator running all the time, I would have to see a drawing of how it was piped to answer that question.  There are piping strategies where the circ would run constantly. 

    Is the house cast iron radiators?  If so then you could have a constant circulation setup and the heat guy is correct in his assumption that the boiler would only fire enough to over come heat loss.  However, I only pipe those systems with a primary/secondary arrangement and a way to keep the space from overheating (ie zone valve).

    My advice would be to contact Buderus to see if they can recommend a factory trained service company in your area to try and sort this out.  It sounds as if a well intentioned technician got in over his head.  Or it could be something as simple as a flow check valve left open.

    If you have a drawing of the piping, email it to me and I would be happy to take a look.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541

    don't need no stinkin "electronic garbage"
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541

    need someone who knows what they are doing or barring that someone with an open mind,mechanical skills and who can read and will let Buderus tech support walk them through it
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • billtwocase
    billtwocase Member Posts: 2,385
    I think

    Slo was talking in a case where an elderly person could freeze to death. It could be as simple as programmable thermostat, to outdoor reset. Some people don't care what they sell, and to whom. When I sell and install, the person currently residing there is what matters, and what is offered as options. I have seen it too many times, the poor or elderly generally don't call when there is a problem. I've found them almost blue. If keeping it simple in those cases is what's best, then so be it. The elderly know how to work a T87. Replace that with today's digital with switches, key pads, and gizmos of the such, and they can be confused rather quickly. For us it's a no brainer
  • Matthew Grallert
    Matthew Grallert Member Posts: 109

    Perhaps you've already solved this issue but there are a few things I see here.  The DWH issue and the overheating issue sound to me like the DWH pump and the heating circuit pump are switched at the Logamatic, that would cause an error to appear.

    Some other things to consider would be a few settings inside the 2107.

    1)BLDG RESP more often then not in this country should be set to 1

    2) The control should recognize there is a room sensor and read RMSETBACK.

    These are just a few things commonly goofed.

    Hope this helps

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