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Buderus DHW prod error

DeanG Member Posts: 13
Happy New Year! I have a buderus G115 boiler and a Logamatic 2107. My house is split between baseboard heat and radiant heated floors in 3 zones. I started getting a DHW prod error a month ago. Happened in the middle of the night and woke up to no heat. I had to switch the Logamatic to manual mode so the zones would heat and my taco relay switch would light up. 

I noticed my temp sensor reading on the buderus wasn’t reading anywhere close to to the actual gauge so we replaced that. It’s reading perfectly now, but I still get the error.

I also noticed that my OA outside sensor isn’t reading correctly either. It says 35 degrees and it’s less than 20 degrees F tonight here in NH, so I’m thinking that may be the next thing to replace.

I had a professional check to make sure the circulator was ok. He verified that the check valve is OK too. I still get the error in manual mode but atleast I still get hot water and heat. 

I’m probably answering my own question by replacing the outside temp sensor next, but are there any experts on here that could give me some words of wisdom? I guess just running on manual mode setting the dial to 140 is best since these Logamatic computers are evil? Thank you 


  • Brent H.
    Brent H. Member Posts: 134
    @DeanG A few thoughts from a fellow Logamatic owner and then maybe one of the pros will chime in. I believe @GW does a bit of work with the Logamatic.

    The OA temperature being off by 15 degrees should not be effecting the hot water production. When hot water is needed, the boiler will increase temperature irregardless of the reset curve/OA sensor to satisfy the hot water demand.

    What I don’t understand is why you’re not getting heat for the house when you get the error. According to the manual, the DHW Err occurs if DHW temp hasn’t increased by 1 degF after 2 hours. The Logamatic should then return control to space heating so your house can get heat instead of the DHW priority preventing it.

    I’m curious, when you get the error, what is the Logamatic is indicating for a DHW temperature? When it is trying to generate DHW, are the pipes to the indirect tank hot? Is there any hot water when you get the error? To me it almost seems like the DHW temp sensor is not functional properly or is not making good contact in the well but that does not explain why the rest of the heating stops working. It is also interesting that you get heat and DHW in manual mode. That proves that the circulators are functional.

    Hopefully one of the pros will have more suggestions. My Logamatic has been very reliable for 10+ years. I’ve only had one issue….. woke up to no heat one morning. After checking the Taco ZC relays and looking at wiring diagrams it turned out my cat had hit the WWSD button on the front. He jumps on the boiler on his way to the top of the DHW tank where he sleeps……😀

  • DeanG
    DeanG Member Posts: 13
    edited January 2022
    Thanks so much for the reply Brent! Got to love cats. My DHW Prod temp says 124 degrees F and the pipes are hot. Basically it would get stuck in DHW prod error then my zones wouldn’t kick on and it would stay in that mode unless I restarted the system. When I get the error in automatic mode I have no heat or hot water but if I switch the automatic switch to (hand) manual mode then set the aquastat to 140 I’m ok. Maybe it’s an issue with my program on the Logamatic. Go figure since I’m a computer science guy and I’ve been fighting this thing for 6 years - I don’t think it saves me any money. :)
  • Brent H.
    Brent H. Member Posts: 134
    Dean, If you have it in manual mode currently at 140, I’d expect the DHW to be at 140 as well if there hasn’t been any hot water used recently. I wonder if it is never reaching temperature for some reason, That still wouldn’t explain why your house zones aren’t heating…… the behavior is really odd and contradict what the manual says.
  • GW
    GW Member Posts: 4,592
    Makes sense, the Control has built-in domestic hot water priority. The only way to override that: I believe you can insert a 242 card, or just build your own controls wire around it.

    If the sensors are ohming correctly, the control may be ready for the dumpster.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • DeanG
    DeanG Member Posts: 13
    edited January 2022
    Thanks GW. I dream about removing the Logamatic. 😂 I’ll check out the 242 card too