diff --git a/src/devices/thermostat.cpp b/src/devices/thermostat.cpp
index f78bf2f60..71b6ccad7 100644
--- a/src/devices/thermostat.cpp
+++ b/src/devices/thermostat.cpp
@@ -557,10 +557,10 @@ uint8_t Thermostat::HeatingCircuit::get_mode_type() const {
     return HeatingCircuit::Mode::DAY;
 }
 
-std::shared_ptr<Thermostat::DhwCircuit> Thermostat::dhw_circuit(const uint8_t offset, const uint8_t dhw_num, const bool create) {
+std::shared_ptr<Thermostat::DhwCircuit> Thermostat::dhw_circuit(const uint8_t offset, const bool create) {
     // check for existing circuit
     for (const auto & dhw_circuit : dhw_circuits_) {
-        if (dhw_circuit->dhw() == dhw_num - 1 || dhw_circuit->offset() == offset) {
+        if (dhw_circuit->offset() == offset) {
             return dhw_circuit;
         }
     }
@@ -568,7 +568,7 @@ std::shared_ptr<Thermostat::DhwCircuit> Thermostat::dhw_circuit(const uint8_t of
         return nullptr;
     }
     // create a new circuit object and add to the list
-    auto new_dhw = std::make_shared<Thermostat::DhwCircuit>(offset, dhw_num == 255 ? offset + 1 : dhw_num);
+    auto new_dhw = std::make_shared<Thermostat::DhwCircuit>(offset);
     dhw_circuits_.push_back(new_dhw);
     // register the device values
     register_device_values_dhw(new_dhw);
@@ -600,7 +600,7 @@ void Thermostat::process_RC10Set(std::shared_ptr<const Telegram> telegram) {
     if (hc == nullptr) {
         return;
     }
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     has_update(telegram, ibaCalIntTemperature_, 0);
     has_update(telegram, backlight_, 1);
     has_update(telegram, dhw->wwMode_, 2);
@@ -867,7 +867,7 @@ void Thermostat::process_IBASettings(std::shared_ptr<const Telegram> telegram) {
 
 // Settings WW 0x37 - RC35
 void Thermostat::process_RC35wwSettings(std::shared_ptr<const Telegram> telegram) {
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     has_update(telegram, dhw->wwProgMode_, 0);     // 0-like hc, 0xFF own prog
     has_update(telegram, dhw->wwCircProg_, 1);     // 0-like hc, 0xFF own prog
     has_update(telegram, dhw->wwMode_, 2);         // 0-off, 1-on, 2-auto
@@ -881,7 +881,7 @@ void Thermostat::process_RC35wwSettings(std::shared_ptr<const Telegram> telegram
 
 // Settings WW 0x3A - RC30
 void Thermostat::process_RC30wwSettings(std::shared_ptr<const Telegram> telegram) {
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     has_update(telegram, dhw->wwMode_, 0);         // 0-on, 1-off, 2-auto
     has_update(telegram, dhw->wwWhenModeOff_, 1);  // 0-off, 0xFF on
     has_update(telegram, dhw->wwDisinfecting_, 2); // 0-off, 0xFF on
@@ -891,7 +891,7 @@ void Thermostat::process_RC30wwSettings(std::shared_ptr<const Telegram> telegram
 
 // type 0x38 (ww) and 0x39 (circ)
 void Thermostat::process_RC35wwTimer(std::shared_ptr<const Telegram> telegram) {
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     if ((telegram->message_length == 2 && telegram->offset < 83 && !(telegram->offset & 1))
         || (!telegram->offset && telegram->type_id == 0x38 && !strlen(dhw->wwSwitchTime_) && telegram->message_length > 1)
         || (!telegram->offset && telegram->type_id == 0x39 && !strlen(dhw->wwCircSwitchTime_) && telegram->message_length > 1)) {
@@ -1004,7 +1004,7 @@ void Thermostat::process_JunkersSetMixer(std::shared_ptr<const Telegram> telegra
 }
 
 void Thermostat::process_JunkersWW(std::shared_ptr<const Telegram> telegram) {
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     has_bitupdate(telegram, dhw->wwCharge_, 0, 3);
 }
 
@@ -1185,7 +1185,7 @@ void Thermostat::process_RC300Curve(std::shared_ptr<const Telegram> telegram) {
 
 // types 0x31B
 void Thermostat::process_RC300WWtemp(std::shared_ptr<const Telegram> telegram) {
-    auto dhw = dhw_circuit(0, 1, true);
+    auto dhw = dhw_circuit(0, true);
     has_update(telegram, dhw->wwSetTemp_, 0);
     has_update(telegram, dhw->wwSetTempLow_, 1);
 }
@@ -1196,7 +1196,7 @@ void Thermostat::process_RC300WWtemp(std::shared_ptr<const Telegram> telegram) {
 void Thermostat::process_RC300WWmode(std::shared_ptr<const Telegram> telegram) {
     uint8_t circuit = 0;
     telegram->read_value(circuit, 0); // 00-no circuit, 01-boiler, 02-mixer
-    auto dhw = dhw_circuit(telegram->type_id - 0x2F5, 255, circuit != 0);
+    auto dhw = dhw_circuit(telegram->type_id - 0x2F5, circuit != 0);
     if (dhw == nullptr) {
         return;
     }
@@ -2105,7 +2105,7 @@ bool Thermostat::set_roomsensor(const char * value, const int8_t id) {
 
 // sets the thermostat ww working mode, where mode is a string, ems and ems+
 bool Thermostat::set_wwmode(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2192,7 +2192,7 @@ bool Thermostat::set_wwtemplow(const char * value, const int8_t id) {
 
 // Set ww charge RC300, ems+
 bool Thermostat::set_wwcharge(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2212,7 +2212,7 @@ bool Thermostat::set_wwcharge(const char * value, const int8_t id) {
 
 // Set ww charge duration in steps of 15 min, ems+
 bool Thermostat::set_wwchargeduration(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2305,7 +2305,7 @@ bool Thermostat::set_switchProgMode(const char * value, const int8_t id) {
 
 // sets the thermostat ww circulation working mode, where mode is a string
 bool Thermostat::set_wwcircmode(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2328,7 +2328,7 @@ bool Thermostat::set_wwcircmode(const char * value, const int8_t id) {
 }
 
 bool Thermostat::set_wwDailyHeating(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2342,7 +2342,7 @@ bool Thermostat::set_wwDailyHeating(const char * value, const int8_t id) {
 }
 
 bool Thermostat::set_wwDailyHeatTime(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2363,7 +2363,7 @@ bool Thermostat::set_wwDailyHeatTime(const char * value, const int8_t id) {
 }
 
 bool Thermostat::set_wwDisinfect(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2384,7 +2384,7 @@ bool Thermostat::set_wwDisinfect(const char * value, const int8_t id) {
 }
 
 bool Thermostat::set_wwDisinfectDay(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -2405,7 +2405,7 @@ bool Thermostat::set_wwDisinfectDay(const char * value, const int8_t id) {
 }
 
 bool Thermostat::set_wwDisinfectHour(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit( id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -3428,7 +3428,7 @@ bool Thermostat::set_switchtime2(const char * value, const int8_t id) {
 }
 // sets a single switchtime in the thermostat dhw program for RC35
 bool Thermostat::set_wwCircSwitchTime(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw == nullptr) {
         return false;
     }
@@ -3445,7 +3445,7 @@ bool Thermostat::set_wwCircSwitchTime(const char * value, const int8_t id) {
 
 // sets a single switchtime in the thermostat circulation program for RC35
 bool Thermostat::set_wwSwitchTime(const char * value, const int8_t id) {
-    auto dhw = dhw_circuit(255, id2dhw(id));
+    auto dhw = dhw_circuit(id2dhw(id));
     if (dhw != nullptr) {
         return false;
     }
@@ -4393,7 +4393,7 @@ void Thermostat::register_device_values() {
     register_device_values_hc(new_hc);
 
     // also a dhw circuit...
-    auto new_dhw = std::make_shared<Thermostat::DhwCircuit>(0, 1); // offset 0, dhw num 1
+    auto new_dhw = std::make_shared<Thermostat::DhwCircuit>(0); // offset 0, dhw num 1
     dhw_circuits_.push_back(new_dhw);
     register_device_values_dhw(new_dhw);
 #endif
@@ -4863,7 +4863,7 @@ void Thermostat::register_device_values_hc(std::shared_ptr<Thermostat::HeatingCi
 
 // registers the values for a heating circuit
 void Thermostat::register_device_values_dhw(std::shared_ptr<Thermostat::DhwCircuit> dhw) {
-    int8_t tag = DeviceValueTAG::TAG_DHW1 + dhw->dhw();
+    int8_t tag = dhw->id();
     switch (this->model()) {
     case EMSdevice::EMS_DEVICE_FLAG_RC100:
     case EMSdevice::EMS_DEVICE_FLAG_RC300:
diff --git a/src/devices/thermostat.h b/src/devices/thermostat.h
index 3643d61b7..0b01687a9 100644
--- a/src/devices/thermostat.h
+++ b/src/devices/thermostat.h
@@ -173,9 +173,8 @@ class Thermostat : public EMSdevice {
 
     class DhwCircuit {
       public:
-        DhwCircuit(const uint8_t offset, const uint8_t dhw_num)
-            : offset_(offset)
-            , dhw_num_(dhw_num) {
+        DhwCircuit(const uint8_t offset)
+            : dhw_num_(offset) {
         }
         ~DhwCircuit() = default;
         uint8_t wwExtra_;
@@ -201,16 +200,16 @@ class Thermostat : public EMSdevice {
         char    wwHoliday_[22];
         char    wwVacation_[22];
 
-        uint8_t dhw() const {
-            return dhw_num_ - 1;
+        uint8_t id() const { // returns TAG(id)
+            return DeviceValueTAG::TAG_DHW1 + dhw_num_;
         }
-        uint8_t offset() const {
-            return offset_;
+
+        uint8_t offset() const { // returns telegram offset
+            return dhw_num_;
         }
 
       private:
-        uint8_t offset_;  // telegram offset to base telegram
-        uint8_t dhw_num_; // dhw circuit number 1..10
+        uint8_t dhw_num_; // dhw circuit number 0..10
     };
 
   private:
@@ -230,8 +229,8 @@ class Thermostat : public EMSdevice {
                 || (model() == EMSdevice::EMS_DEVICE_FLAG_CR120));
     }
 
-    inline uint8_t id2dhw(const int8_t id) const {
-        return id - DeviceValueTAG::TAG_DHW1 + 1;
+    inline uint8_t id2dhw(const int8_t id) const { // returns telegram offset for TAG(id)
+        return id - DeviceValueTAG::TAG_DHW1;
     }
 
     // each thermostat has a list of heating controller type IDs for reading and writing
@@ -394,7 +393,7 @@ class Thermostat : public EMSdevice {
 
     std::shared_ptr<Thermostat::HeatingCircuit> heating_circuit(std::shared_ptr<const Telegram> telegram);
     std::shared_ptr<Thermostat::HeatingCircuit> heating_circuit(const int8_t id);
-    std::shared_ptr<Thermostat::DhwCircuit>     dhw_circuit(const uint8_t offset = 0, const uint8_t dhw_num = 255, const bool create = false);
+    std::shared_ptr<Thermostat::DhwCircuit>     dhw_circuit(const uint8_t offset, const bool create = false);
 
     void register_device_values_hc(std::shared_ptr<Thermostat::HeatingCircuit> hc);
     void register_device_values_dhw(std::shared_ptr<Thermostat::DhwCircuit> dhw);