diff --git a/ha-thermostat-calibration.yaml b/ha-thermostat-calibration.yaml
index edb469f..18b57ff 100644
--- a/ha-thermostat-calibration.yaml
+++ b/ha-thermostat-calibration.yaml
@@ -105,50 +105,57 @@ action:
             climate_device: "{{ device_id(climate_entity) }}"
             external_temp: "{{ states(external_sensor) | float(0) }}"
             valve_temp: "{{ state_attr(climate_entity, 'current_temperature') | float(0) }}"
-        
-        # Skip if climate entity is unavailable or has no valid temperature
+            hvac_action: "{{ state_attr(climate_entity, 'hvac_action') }}" # Get valve state (heating/idle)
+            target_temp: "{{ state_attr(climate_entity, 'temperature') | float(0) }}" # Get setpoint
+
+        # 1. Standard Skip Conditions
         - condition: template
           value_template: >
             {{ states(climate_entity) not in ['unknown', 'unavailable'] and valve_temp > 0 and external_temp > 0 }}
-        
-        # Find offset entity for this device
+
+        # 2. **CRITICAL STABILITY CONDITION**
+        # Only calibrate if the valve is not actively heating and the setpoint is close to external temp
+        - condition: template
+          value_template: >
+            {{ hvac_action != 'heating' and (target_temp - external_temp) < 0.5 }}
+
+        # Find offset entity for this device (unchanged)
         - variables:
             offset_entity: >
               {% set entities = device_entities(climate_device) if climate_device else [] %}
               {% set offset_entities = entities | select('match', '^number\.') | select('search', offset_entity_suffix) | list %}
               {{ offset_entities[0] if offset_entities else '' }}
         
-        # Skip if no offset entity found or is unavailable
+        # 3. Skip if no offset entity found (unchanged)
         - condition: template
           value_template: "{{ offset_entity != '' and states(offset_entity) not in ['unknown', 'unavailable'] }}"
         
-        # Calculate and set new offset
+        # 4. Calculate New Offset using Differential Method
         - variables:
             current_offset: "{{ states(offset_entity) | float(0) }}"
             
-            # 1. Calculate the required offset based on the difference
-            # Required Offset = External Temp - (Valve Internal Temp - Current Offset) + Manual Correction
-            raw_offset_required: "{{ external_temp - (valve_temp - current_offset) + manual_correction }}"
+            # The new required offset is the difference between the external (ground truth)
+            # and the uncompensated internal sensor reading.
+            raw_offset_required: "{{ external_temp - valve_temp + manual_correction }}"
             
-            # 2. Round the raw offset to the nearest rounding_step
-            # Safely scale, round, and scale back to minimize floating point errors
+            # Round the raw offset to the nearest rounding_step (unchanged rounding logic)
             new_offset: >
               {% set step = rounding_step | float(1.0) %}
               {% set scale = (1 / step) | round(0) %}
               {{ (raw_offset_required * scale) | round(0) / scale }}
         
-        # Only update if the calculated value is different from the current value
+        # 5. Only update if the calculated value is different from the current value (unchanged)
         - condition: template
           value_template: "{{ new_offset | round(3) != current_offset | round(3) }}"
         
-        # Set new offset
+        # 6. Set new offset (unchanged)
         - service: number.set_value
           target:
             entity_id: "{{ offset_entity }}"
           data:
             value: "{{ new_offset }}"
         
-        # Small delay between updates to avoid overwhelming the system
+        # Small delay between updates (unchanged)
         - delay:
             milliseconds: 100