No possibility to control the boiler temperature via 'selflowtemp' Junkers GC2200W

[jlk3281]

Hi,
I have a Junkers ACU-LOP13/Logamax Plus GB122, Condense 2300, and Junkers Cerapur GC2200W.

I don't have any physical thermostats.

I use https://bbqkees-electronics.nl/product/ems-interface-board-v3-1/ to control my stove.

So far, I've been using my own automations for the heating curve to control:

• heating activation (heatingactivated)
• burner delay (burnminperiod)
• hysteresis (boilhyston, boilhystoff)
• flow temperature (heatingtemp)

Now I'd like to use the thermostat https://github.com/Alexwijn/SAT to use the heating curve.

And here's the problem...
SAT sends telegrams:

[command] Called command boiler/heatingoff (wymuś wyłączenie grzania) with value off
[command] Called command boiler/selfflowtemp (wybrana temperatura zasilania) with value 55.00
[command] Called command boiler/burnmaxpower (maksymalna moc źródła ciepła) with value 100

So it tries to do 'selfflowtemp'
but it doesn't affect my furnace at all; no change occurs. The furnace heats to the temperature set by 'heatingtemp'.
Below are additional logs:

2025-10-02T11:49:14.959129+02:00 ems-esp command 003+18:12:47.980 I 371902: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 37
2025-10-02T11:49:15.060234+02:00 ems-esp emsesp 003+18:12:48.087 T 371903: me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 25
2025-10-02T11:49:17.100205+02:00 ems-esp emsesp 003+18:12:50.117 T 371904: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27
2025-10-02T11:49:17.323624+02:00 ems-esp emsesp 003+18:12:50.169 T 371905: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: 00 2D 2D 00 00 CB 00 00 F7 00 00 00 02 00 F5 00 00 00 00 00 00 FF 00 00 F7 00 00
2025-10-02T11:49:17.421656+02:00 ems-esp emsesp 003+18:12:50.169 T 371906: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27 (offset 27)
2025-10-02T11:49:17.525546+02:00 ems-esp emsesp 003+18:12:50.169 T 371907: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: 00 00 00 00 00 00 00 (offset 35)
2025-10-02T11:49:17.621803+02:00 ems-esp emsesp 003+18:12:50.169 T 371908: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27 (offset 42)
2025-10-02T11:49:17.721683+02:00 ems-esp emsesp 003+18:12:50.169 T 371909: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: <empty> (offset 42)
2025-10-02T11:49:20.079005+02:00 ems-esp emsesp 003+18:12:53.107 T 371910: boiler(0x08) B all(0x00), UBAMonitorSlowPlus2(0xE3), data: 04 00 00 00 00 00 00 00 00 00 00 00 F8 00 64 22 00 00 00 2A
2025-10-02T11:49:20.429482+02:00 ems-esp emsesp 003+18:12:53.314 T 371911: boiler(0x08) B all(0x00), UBAMonitorFastPlus(0xE4), data: 00 2D 2D 00 00 CB 00 00 F8 00 00 00 02 00 F5 00 00 00 00 00 00 FF 00 00 F8 00 00
2025-10-02T11:49:20.525025+02:00 ems-esp emsesp 003+18:12:53.502 T 371912: boiler(0x08) B all(0x00), UBAMonitorFastPlus(0xE4), data: 00 00 00 00 00 00 00 (offset 35)
2025-10-02T11:49:20.853814+02:00 ems-esp emsesp 003+18:12:53.733 T 371913: boiler(0x08) B all(0x00), UBAMonitorWWPlus(0xE9), data: 2A 01 06 80 00 00 00 01 06 46 00 00 00 02 00 91 62 00 4D 4B 00 00 00 2A 01
2025-10-02T11:49:20.954121+02:00 ems-esp emsesp 003+18:12:53.984 T 371914: me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 00 00 00 00
2025-10-02T11:49:30.040203+02:00 ems-esp emsesp 003+18:13:03.069 T 371915: boiler(0x08) B all(0x00), UBADevices(0x07), data: 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00
2025-10-02T11:49:30.221892+02:00 ems-esp emsesp 003+18:13:03.253 T 371916: boiler(0x08) B all(0x00), ?(0xC4), data: 00
2025-10-02T11:49:30.403887+02:00 ems-esp emsesp 003+18:13:03.434 T 371917: boiler(0x08) B all(0x00), UBAOutdoorTemp(0xD1), data: 7F FF

The logs show that the furnace can't determine the outside temperature, and it can't because I don't have an external sensor connected (Junkers AF2). Maybe that's the problem, the 'selfflowtemp' setting doesn't work? Maybe I actually need that sensor?

Request for help
topics that I have already started in other places:

• SAT integration with ems-esp junkers/bosch - bad call command Alexwijn/SAT#106
• https://discord.com/channels/816637840644505620/816652040305901628/1422520133376675902

Below is a detailed description of the furnace and the ems-esp software:

Device:

ems-esp:$ show devices
These EMS devices are currently active:

Kocioł: Junkers ACU-LOP13/Logamax Plus GB122, Condense 2300, Junkers Cerapur GC2200W (DeviceID:0x08, ProductID:234, Version:05.05) (82)
 Received telegram type IDs: 0xBF 0xC2 0x14 0x15 0xD1 0xE3 0xE4 0xE5 0xE9 0x2E 0x04 
 Fetched telegram type IDs: 0xE6 0xEA 0x28 
 Pending telegram type IDs: 0x10 0x11 0x1C 0x18 0x19 0x1A 0x35 0x16 0x33 0x34 0x26 0x2A 0x3B 
 Ignored telegram type IDs: 0xC4 0xDAC 0x17 

System:

ems-esp:$ show

System:
 Version: 3.7.2
 Platform: ESP32 (ESP32-D0WDQ6)
 Model: 
 Partition: app0
 Language: pl
 Board profile: S32
 Uptime: 003+17:57:29.617
 Base MAC Address: 9C:9C:1F:D5:7C:4C
 SDK version: 4.4.8.240628
 CPU frequency: 240 MHz
 Free heap/Max alloc: 167 KB / 107 KB
 App used/free: 1650 KB / 334 KB
 FS used/free: 24 KB / 40 KB
 Flash size: 4096 KB
 PSRAM: not available

[MichaelDvP]

me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 00 00 00 00

Looks like you have set forceheatingoff

[jlk3281]

Boiler/HeatingOff is set to 'off' by SAT.
I set 'forceheatingOff' in ems-esp (GUI) to 'on' but also to 'off'. I tested it in both situations, and it didn't change anything.

I disabled forceheatingOff

2025-10-02T12:50:27.421418+02:00 ems-esp command 003+19:14:00.491 I 374955: Called command boiler/heatingoff (wymuś wyłączenie grzania) with value wyłączono
2025-10-02T12:50:27.510748+02:00 ems-esp emsesp 003+19:14:00.531 T 374956: me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 22 32 64 00
2025-10-02T12:50:34.688536+02:00 ems-esp emsesp 003+19:14:07.762 T 374957: boiler(0x08) B all(0x00), UBADevices(0x07), data: 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00
2025-10-02T12:50:34.870161+02:00 ems-esp emsesp 003+19:14:07.948 T 374958: boiler(0x08) B all(0x00), ?(0xC4), data: 00
2025-10-02T12:50:35.196876+02:00 ems-esp emsesp 003+19:14:08.129 T 374959: boiler(0x08) B all(0x00), UBAOutdoorTemp(0xD1), data: 7F FF

test:

$ curl  -H "Content-Type: application/json" -X POST -H 'Authorization: Bearer TOKEN' http://ENDPONIT/api/boiler/selflowtemp -d '{"value": 37}'
{}

log:

2025-10-02T12:52:24.384552+02:00 ems-esp command 003+19:15:57.456 I 375098: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 37
2025-10-02T12:52:24.483393+02:00 ems-esp emsesp 003+19:15:57.504 T 375099: me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 25
2025-10-02T12:52:24.925566+02:00 ems-esp emsesp 003+19:15:58.005 T 375100: boiler(0x08) B all(0x00), UBAMonitorSlowPlus2(0xE3), data: 04 00 00 00 00 00 00 00 00 00 00 00 F8 00 64 22 00 00 00 2A
2025-10-02T12:52:25.270284+02:00 ems-esp emsesp 003+19:15:58.202 T 375101: boiler(0x08) B all(0x00), UBAMonitorFastPlus(0xE4), data: 00 2D 2D 00 00 CB 00 00 F8 00 00 00 02 00 F6 00 00 00 00 00 00 FF 00 00 F8 00 00
2025-10-02T12:52:25.367137+02:00 ems-esp emsesp 003+19:15:58.392 T 375102: boiler(0x08) B all(0x00), UBAMonitorFastPlus(0xE4), data: 00 00 00 00 00 00 00 (offset 35)
2025-10-02T12:52:25.543530+02:00 ems-esp emsesp 003+19:15:58.622 T 375103: boiler(0x08) B all(0x00), UBAMonitorWWPlus(0xE9), data: 2A 00 EE 80 00 00 00 00 EE 46 00 00 00 02 00 91 62 00 4D 4B 00 00 00 2A 01
2025-10-02T12:52:26.566719+02:00 ems-esp emsesp 003+19:15:59.647 T 375104: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27
2025-10-02T12:52:26.668282+02:00 ems-esp emsesp 003+19:15:59.685 T 375105: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: 00 2D 2D 00 00 CB 00 00 F8 00 00 00 02 00 F6 00 00 00 00 00 00 FF 00 00 F8 00 00
2025-10-02T12:52:26.770172+02:00 ems-esp emsesp 003+19:15:59.685 T 375106: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27 (offset 27)
2025-10-02T12:52:26.875217+02:00 ems-esp emsesp 003+19:15:59.724 T 375107: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: 00 00 00 00 00 00 00 (offset 35)
2025-10-02T12:52:26.970167+02:00 ems-esp emsesp 003+19:15:59.724 T 375108: me(0x0B) R boiler(0x08), UBAMonitorFastPlus(0xE4), length: 27 (offset 42)
2025-10-02T12:52:27.071172+02:00 ems-esp emsesp 003+19:15:59.747 T 375109: boiler(0x08) W me(0x0B), UBAMonitorFastPlus(0xE4), data: <empty> (offset 42)

value:

$ curl -s http://ADDRESS_EMS_ESP/api/boiler/selfflowtemp | jq .value
0

I had the furnace set this way and it still didn't respond to 'selflowtemp' but to 'heatingtemp'

[MichaelDvP]

I don't know what you have set on your boiler and how the system is configured, but if you read here you should know that heatingtemp is:

• the upper limit for selflowtemp, you can't set selflowtem to a higer value than heatingtemp.
• the fallback after 1-2 min if selflowtemp is not updated. You need to update selflowtemp every minute, otherwise the boiler timeout an set heatingstemp as actual flow temp.

[jlk3281]

Yes, I have it set as you describe, i.e., 'heatingtemp': 42 degrees Celsius (upper limit) and 'selflowtemp': 40 degrees Celsius, sent periodically by SAT. See below, SAT sends it even more frequently than every minute.

And note... the furnace heats to 42 degrees Celsius + boilhystoff (hysteresis), not 40 degrees Celsius + boilhystoff (hysteresis)

root@nas ~ $ curl -s  http://ENDPOINT_EMS_ESP/api/boiler/heatingtemp  | jq .value
42

root@nas ~ $ tail -f /var/log/syslog | grep selflowtemp
2025-10-03T11:16:24.851178+02:00 ems-esp command 000+14:00:47.697 I 58625: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:28.737126+02:00 ems-esp command 000+14:00:51.273 I 58641: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:31.890647+02:00 ems-esp command 000+14:00:54.266 I 58655: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:34.938322+02:00 ems-esp command 000+14:00:57.843 I 58671: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:35.143454+02:00 ems-esp command 000+14:00:58.048 I 58673: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:39.591902+02:00 ems-esp command 000+14:01:01.844 I 58698: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:45.481218+02:00 ems-esp command 000+14:01:07.972 I 58727: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:16:48.674432+02:00 ems-esp command 000+14:01:11.024 I 58743: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:03.832148+02:00 ems-esp command 000+14:01:26.821 I 58769: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:04.849495+02:00 ems-esp command 000+14:01:27.839 I 58773: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:11.153561+02:00 ems-esp command 000+14:01:33.294 I 58807: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:18.007669+02:00 ems-esp command 000+14:01:40.994 I 58842: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:24.986126+02:00 ems-esp command 000+14:01:47.920 I 58860: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:28.676141+02:00 ems-esp command 000+14:01:51.096 I 58876: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:17:34.991114+02:00 ems-esp command 000+14:01:57.885 I 58894: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00

and response from esp:

2025-10-03T11:21:52.306486+02:00 ems-esp command 000+14:06:14.752 I 59918: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-03T11:21:52.407396+02:00 ems-esp emsesp 000+14:06:14.800 T 59919: me(0x0B) W boiler(0x08), UBASetPoints(0x1A), data: 28

Below is everything that is set on my boiler:

Kocioł: Junkers ACU-LOP13/Logamax Plus GB122, Condense 2300, Junkers Cerapur GC2200W (DeviceID:0x08, ProductID:234, Version:05.05) (82)
  wymuś wyłączenie grzania (heatingoff): wyłączono 
  c.o. aktywne (heatingactive): włączono 
  c.w.u. aktywne (tapwateractive): wyłączono 
  wybrana temperatura zasilania (selflowtemp): 42 °C
  wysterowanie pompy c.o. (heatingpumpmod): 100 %
  temperatura zasilania (curflowtemp): 36.7 °C
  sprzęgło hydrauliczne (headertemp): 0.0 °C
  temperatura spalin (exhausttemp): 16.9 °C
  gaz (burngas): włączono 
  prąd palnika (flamecurr): 20.0 µA
  wentylator (fanwork): włączono 
  zapłon (ignwork): wyłączono 
  minimalna moc źródła ciepła (burnminpower): 19 %
  maksymalna moc źródła ciepła (burnmaxpower): 50 %
  minimalny czas pracy palnika (burnminperiod): 30 
  aktualna moc źródła ciepła (absolutna) (absburnpow): 19 %
  blok grzewczy (heatblock): 36.5 °C
  histereza załączania (boilhyston): -4 °C
  histereza wyłączania (boilhystoff): 4 °C
  heatingcurve on (curveon): wyłączono 
  heatingcurve base (curvebase): 25 °C
  heatingcurve end (curveend): 45 °C
  temperatura przełączania lato/zima (summertemp): 16 °C
  temperatura wiodąca dla ochrony przed zamarzaniem (nofrostmode): wyłączono 
  temperatura ochrony przed zamarzaniem (nofrosttemp): 5 °C
  system c.o. (heatingactivated): włączono 
  temperatura grzania (heatingtemp): 42 °C
  pompa ciepła (heatingpump): włączono 
  maksymalna moc pompy zasobnika (pumpmodmax): 100 %
  minimalna moc pompy zasobnika (pumpmodmin): 1 %
  charakterystyka pompy kotłowej (pumpcharacter): proporcjonalny 
  wybrana moc źródła ciepła (selburnpow): 100 %
  aktualna moc źródła ciepła (curburnpow): 38 %
  liczba uruchomień palnika (burnstarts): 32791 
  łączny czas pracy palnika (burnworkmin): 89 dni 14 godzin 52 minut 
  łączny czas pracy palnika 2 stopnia (burn2workmin): 0 dni 0 godzin 0 minut 
  łączny czas grzania (heatworkmin): 63 dni 18 godzin 18 minut 
  liczba uruchomień palnika na ogrzewanie (heatstarts): 12996 
  łączny czas pracy układu sterowania (ubauptime): 1323 dni 19 godzin 14 minut 
  ostatni błąd (lastcode):  --(2967) @uptime 1899361 - 1899364 min 
  kod serwisowy (servicecode): -- 
  numer kodu serwisowego (servicecodenumber): 200 
  rodzaj przeglądu (maintenance): data 
  czas do kolejnego przeglądu (maintenancetime): 6000 godzin
  termin następnego przeglądu (maintenancedate): 25.10.2025 
  praca w trybie awaryjnym (emergencyops): wyłączono 
  temperatura w trybie awaryjnym (emergencytemp): 40 °C
  Flow PC0 (pc0flow): 0 l/h
  licznik ogrzewania (meterheat): 0.0 kWh
  CWU licznik (meter): 0.0 kWh
  licznik gazu na ogrzewanie (gasmeterheat): 7192.3 kWh
  CWU licznik gazu (gasmeter): 5234.1 kWh
  CWU temperatura zadana (settemp): 42 °C
  CWU temperatura wyższa/komfort (seltemp): 42 °C
  CWU temperatura niższa/eko (seltemplow): 35 °C
  CWU temperatura dodatkowej ciepłej wody (seltempsingle): 0 °C
  CWU tryb komfortu (comfort1): eko 
  CWU korekta temperatury wypływu (flowtempoffset): 0 °C
  CWU optymalizacja grzania (chargeoptimization): wyłączono 
  CWU temperatura maksymalna (maxtemp): 54 °C
  CWU pompa cyrkulacji zainstalowana (circpump): wyłączono 
  CWU histereza załączania (hyston): 0 °C
  CWU histereza wyłączania (hystoff): 0 °C
  CWU temperatura dezynfekcji termicznej (disinfectiontemp): 70 °C
  CWU tryb pracy cyrkulacji (circmode): wyłączono 
  CWU pompa cyrkulacji (circ): wyłączono 
  CWU temperatura zasobnika (curtemp): 31.5 °C
  CWU aktualny przepływ (curflow): 0.0 l/min
  CWU system przygotowywania c.w.u. (activated): włączono 
  CWU jednorazowa dodatkowa ciepła woda (onetime): wyłączono 
  CWU dezynfekcja termiczna (disinfecting): wyłączono 
  CWU grzanie (charging): wyłączono 
  CWU ponowne grzanie (recharging): wyłączono 
  CWU temperatura OK (tempok): wyłączono 
  CWU zawór 3-drogowy aktywny (3wayvalve): wyłączono 
  CWU liczba załączeń (starts): 19795 
  CWU czas aktywności (workm): 25 dni 20 godzin 34 minut 
  moc nominalna (nompower): 20 kW
  całkowita energia (nrgtotal): 6759.70 kWh
  energia na ogrzewanie (nrgheat): 3455.82 kWh
  CWU energia (nrg): 3303.87 kWh

When the above data is uploaded, the self-low temperature is still set to 40 degrees by SAT, but as you can see, the value there does not change:

 wybrana temperatura zasilania (selflowtemp): 42 °C

is exactly as set in 'heatingtemp' at all times.

I also manually performed a POST on selflow every minute with a value lower than heatingtemp and the furnace still heated up to the 'heatingtemp' value

[MichaelDvP]

Don't know what this is, but seems the newer ems+ boilers uses a different command telegram.
I can't find a log from this boiler with thermostat attached, but i guess it could be telegram 0xE7.
Please check if selflowtemp command works for you with software https://github.com/MichaelDvP/EMS-ESP32/releases/tag/latest

[jlk3281]

I uploaded the EMS-ESP-3_7_3-dev_18-ESP32-4MB.bin firmware

2025-10-04T13:07:36.867030+02:00 ems-esp command 000+00:10:34.947 I 2027: Called command boiler/selflowtemp (wybrana temperatura zasilania) with value 40.00
2025-10-04T13:07:36.970347+02:00 ems-esp emsesp 000+00:10:34.947 T 2028: me(0x0B) W boiler(0x08), ?(0xE7), data: 28

root@nas ~ $curl -s http://ENDPOINT_EMS_ESP/api/boiler/selflowtemp | jq .value
42

[jlk3281]

@MichaelDvP Thank you very much for your help. If the SAT doesn't work, I'll still be using my own device to control the boiler. Thanks again, and I think this thread can be closed.

[enricoschroeder]

Hi! While debugging a similar issue (Alexwijn/SAT#109) I tried your development firmware (where you changed the telegram for selflowtemp). Please note that this breaks the setting on my Bosch Condens 7000i - it only works with the "old" telegram used in the latest release version (which is why I needed to revert to the old version).

Also, I am working on fixing the described issue in SAT to improve EMS support (see enricoschroeder/SAT@8fce77d)

[MichaelDvP]

"old" is very unspecific. In https://github.com/MichaelDvP/EMS-ESP32/releases/tag/latest i have added back the ems setting telegram (0x1A) for ems+ boilers. I guess this what you mean.
Regarding enricoschroeder/SAT@8fce77d i think selflowtemp setting to 0 works, this is what heatingoff command do. Maybe the values 1-12 does not work? replace {max(12, value} by {value < 12 ? 0 : value}. The selburnpower (line 138) command is right, but i think DATA_MAX_REL_MOD_LEVEL_SETTING = "burnmaxpower" is for reading the limit, so this should stay on burmaxpower. But maybe i'm wrong.

[enricoschroeder]

Thanks for the feedback! By "old" I mean the current release version 3.7.2. With this it works. With the development release posted above it does not. I was referring to this comment:

Transmission mode is only timing, if you get many tx-errors reported try a different mode.

I've searched logs for ems+boilers with thermostats, maybe i've found the right telegram, I've updated https://github.com/MichaelDvP/EMS-ESP32/releases/tag/latest, please download, flash and check. Log should now show: me(0x0B) W boiler(0x08), ?(0x2E0), data: 28 (offset 1)

[MichaelDvP]

Ok, than i have understood right and 8a4e6d5 fixes this.