Logamatic setback problem

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jrr

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I have trying to get a Logamatic 2107 night setback to work on a BFU controlled mixed circuit on a Boderus G115WS. Instead of setting the temperature back, the boiler just stops firing at the setback time until about 3AM when the boiler temperature has fallen to about 68. I can't believe that the unit isn't defective. At this point I have narrowed it down by setting up the Logamatic simply as follows:
  • CIRCUIT 1 set to NO-SYSTEM, so that it cannot interfere with the setback (I do have a couple of thermostatically controlled zones but for these experiments I have told the Logamatic that there nothing connected to the higher temperature)
  • DHW has been set to AUT, so that it should not kick in during the night setback (or at least not unit the last 30 minutes of the setback period)
  • CIRCUIT 2 set to PERIM-HTG, REF TEMP 145, MAX TEMP2 160, REMOTE 2 ON, ROOMCOMP 6, RMSETBACK, OFFSET 0
  • Program 2 is set to SENIOR (10PM-5:30AM night setback)
  • Boiler: BLDG RESP 1, PUMPLOGIC 104, MAX TEMP 180, FREEZETEMP 41
  • BFU2: dial set to 72, and BFU setback switch set to 1 (i.e., 1.8 degrees for this test, so should only set back to 70) and HK set to 2
In manual day mode the system works great, and I can dial back the temperature at night without a problem. I have oversized cast iron radiators that used to overshoot with my old boiler, and the Logamatic and the mixing valve on circuit 2 keeps things very steady. So it would be great if the night setback also worked! Another weird this is that if I wake up at 2AM, if I power cycle the Logamatic it seems to start working again. Also, it seems that the heating curve 2 shown on the LCD is correct -- 50-86, 32-111, and 14-133 -- and the outdoor temperature shows correctly (e.g., 30) -- it's just not being followed).

Does anyone see anything that could be wrong with the setting that would cause the boiler to turn off rather than set back by a few degrees?

I've contacted Bosch, but it seems they are stumped and/or haven't found someone who can spot what's wrong.

Thanks,

Robin
 

fitter30

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Room set back have a room sensor? When cycling power will reset any failures or conflicts. Never worked on this.control I'll let look.at tomorrow when im fresh. Where this control tied into the boiler?
 

jrr

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A Bosch BFU (HS2105) room sensor is connected to a FM241 mix controller in the Logamatic 2107 (pretty much like Example 8.7 in the Applications Manual) -- works great except for the automatic setback mode. In fact, I replaced the BFU because I thought it might be bad with no change. So this seems like a Logamatic specific issue, and more specifically a room-sensor-based programmed setback.
 

jrr

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I am not sure if you mean the BFU room sensor setting in the rotary switch. I have tried #1, #3 and #4 -- all the same -- it's currently at #1=1.8 degreesF. I am attaching a photo of my BFU and the manual page I am relying on.
 

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jrr

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I went back and read the notes in the Application Manual for Example 8.7 -- I see that is says something curious:

HK2 circuit (mixed temperature)
• Mixed water temperature is maintained based on the selected heating curve and input from the outdoor sensor (FA), supply sensor (FV) and room sensor.
• During setback periods, the boiler temperature will be reduced based on the night setback setting on the room sensor.
• Power to the PH-HK2 circuit is turned off under the following conditions:
1) Initial part of night setback period
2) Condensate protection
3) Outdoor temperature exceeds WWSD setpoint
• This application requires a room sensor for radiant floor heating.


So it seems that the "initial part of night setback period" is lasting way too long -- I don't see what is supposed to end that period.
 

jrr

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I don't think there is an issue here, but I drew up the wiring diagram of how the system is set up right now...
 

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jrr

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I've been monitoring the boiler, mix, and room temperature so you can see that the boiler just shuts down when the night period starts...
 

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