Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Buderus Logmatic HS2109 help

So many questions but I will try to be specific. I have a Buderus G215 Oil boiler sitting on top of a Buderus LT Indirect DHW heater. Controlling it is a Logmatic HS2109 (The temperature readout is not digital). I've been trouble shooting it lately because it seems sometimes that the Heating Circulator does not run or the Tank Circulator for the DHW does not run. Instead of writing a whole book here I just have some specific questions. I'll preface this by saying that I've gone through the Logmatic instructions and have looked at the wiring terminal diagrams and the function of each terminal.

1. Does the Heat Circulating terminal have any sensor associated with it like the Tank Circulator does? If not then I assume the terminal is turned on or off based on some type of other logic.

2. What is the draw back in setting Switch 2 on the jumpers to "No DHW Priority" other than possible Longer heat-up times for DHW?

When we bought the house the previous owner mentioned that sometimes the heat circulator would not run so just to shut off the boiler switch wait about a minute and turn it back on. After doing this a couple times and then at one point the on and off was not even working I started troubleshooting and found the problems went back to the controller. The controller has power going to it and it works when you turn the dial to raise the boiler temp (i.e. it fires the boiler) but last night for the life of me I could not get DHW or Heat Circulator pumps to start working. I pulled off the Logmatic cover, took out my voltage tester and tested the terminals. The boiler burner terminals had power as expected however the Heat Circulator and Tank Circulator terminals had no power. Turning things on and off were not doing anything. I tried everything from turning on all my thermostats, to running the water in my shower and faucets, (all things I was just guessing at) to get those pumps to start.

Now the way I got the DHW circ to start working was totally by accident. While testing the terminals in the Logmatic, I put my voltage tester on the Tank Sensor terminals, I then heard a little static as in I shorted a connection. The Tank Circulator pump kicked on! Just to be sure I put my voltage meter back on the Tank Circulator terminal and saw that I had power. I was thrilled because it all started to make sense. I am guessing that by shorting the Tank sensor terminal with my volt meter it gave a signal for the tank circulator to turn on. I followed the wires for the Tank Sensor and saw that the sensor was mounted on the hot water supply pipe coming out of the DHW tank with foil wrapped around it rather than on the front of the DHW tank like it is supposed to be. So I think the problem here might be the sensor as opposed to the terminal or the something on the circuit board (at least I hope).

However my Heat Circulator was still not working. I then remember the owner saying that the system was set for DHW Priority. He told me that there will be no heat to the rest of the house until DHW is satisfied. So I'm thinking how does it know when DHW is satisfied? I realized it has to be that same sensor that is attached to the DHW supply pipe which at this point is still cold. At this point the house was getting colder so I was desperate to get the heat circulator started. I thought about just removing the wiring the pump wiring from the Logmatic terminal and just splicing it to a electrical plug and just plugging into a wall outlet, however I then came across enabling the terminal by changing the jumpers for Switch 2 to No DHW Priority. Once I did that the circulator came on and I verified it again with my volt meter.

So now things are working however I don't like the fact that I had to make those changes. After the season I will get a Buderus tech out here to service the system and perhaps properly mount the Tank Sensor since that is what seems to be the cause of all this. (Well it's either that or the Logmatic is going bad I think)

Are there any problems with how this is running now? Sorry I guess I did write a whole book...


  • heathead
    heathead Member Posts: 189
    The Logomatic has some program in it to make sure the boiler is above a certain Temp ? 114 before it will allow the DHW or the heating circulator pump to turn on it protects the boiler. You need to check the sensor in the boiler and wiring to it and make sure it is reading to correct temperature.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,451
    The 2109 is just a glorified triple aquastat, no reset capability. I'd lose it for a 2107 or just go to a AquaSmart or Hydrostat
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    Bob Bona_4Zman
  • 336mlk
    336mlk Member Posts: 17
    Hey heathead... Yes I saw that. It is actually 113. How do you check a sensor? Can I take the wires and plug it into another device that shows what the temperature is.

    Robert I was thinking to replace it as well. I wonder if I can just swap it out myself or if I need to get a certified tech. I mean looking at the current system and the instructions it wasn't exactly rocket science, but I'm not from an HVAC background but am from an I.T. background.
  • 336mlk
    336mlk Member Posts: 17
    I just read about the 2109. And it seems really advanced compared to the 2107 but I realized that the I also have a Central Boiler Wood furnace that also sends hot water to Buderus Boiler. The pump for the wood boiler basically runs 24 x 7 and the water temp is whatever is set on the wood boiler. I wouldn't be able to use all the fancy settings of the 2107 because the Logmatic has no control on how the wood boiler works, and since the wood boiler is the primary source for heat I guess there wouldn't me that much benefit from the advanced features of the 2107.