diff --git a/custom_components/versatile_thermostat/underlyings.py b/custom_components/versatile_thermostat/underlyings.py
index b39ac45..283ece7 100644
--- a/custom_components/versatile_thermostat/underlyings.py
+++ b/custom_components/versatile_thermostat/underlyings.py
@@ -1158,7 +1158,8 @@ class UnderlyingValveRegulation(UnderlyingValve):
         if self.have_closing_degree_entity:
             await self._send_value_to_number(
                 self._closing_degree_entity_id,
-                closing_degree := self._max_opening_degree - self._percent_open,
+                # Patch to fix the hvac_action always Idle issue (issue #902)
+                closing_degree := max(self._max_opening_degree - 1 - self._percent_open, 0),
             )
 
         # send offset_calibration to the difference between target temp and local temp
diff --git a/tests/test_overclimate_valve.py b/tests/test_overclimate_valve.py
index a29cd4c..a57657c 100644
--- a/tests/test_overclimate_valve.py
+++ b/tests/test_overclimate_valve.py
@@ -139,7 +139,7 @@ async def test_over_climate_valve_mono(hass: HomeAssistant, skip_hass_states_get
         mock_service_call.assert_has_calls(
             [
                 call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree'}),
-                call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree'}),
+                call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree'}),
                 call("climate","set_temperature",{
                         "entity_id": "climate.mock_climate",
                         "temperature": 15,  # temp-min
@@ -188,7 +188,7 @@ async def test_over_climate_valve_mono(hass: HomeAssistant, skip_hass_states_get
             [
                 call('climate', 'set_temperature', {'entity_id': 'climate.mock_climate', 'temperature': 19.0}),
                 call(domain='number', service='set_value', service_data={'value': 40}, target={'entity_id': 'number.mock_opening_degree'}),
-                call(domain='number', service='set_value', service_data={'value': 60}, target={'entity_id': 'number.mock_closing_degree'}),
+                call(domain='number', service='set_value', service_data={'value': 59}, target={'entity_id': 'number.mock_closing_degree'}),
                 # 3 = 18 (room) - 15 (current of underlying) + 0 (current offset)
                 call(domain='number', service='set_value', service_data={'value': 3.0}, target={'entity_id': 'number.mock_offset_calibration'})
             ]
@@ -234,7 +234,7 @@ async def test_over_climate_valve_mono(hass: HomeAssistant, skip_hass_states_get
         mock_service_call.assert_has_calls(
             [
                 call(domain='number', service='set_value', service_data={'value': 13}, target={'entity_id': 'number.mock_opening_degree'}),
-                call(domain='number', service='set_value', service_data={'value': 87}, target={'entity_id': 'number.mock_closing_degree'}),
+                call(domain='number', service='set_value', service_data={'value': 86}, target={'entity_id': 'number.mock_closing_degree'}),
                 # 6 = 18 (room) - 15 (current of underlying) + 3 (current offset)
                 call(domain='number', service='set_value', service_data={'value': 6.899999999999999}, target={'entity_id': 'number.mock_offset_calibration'})
             ]
@@ -280,7 +280,7 @@ async def test_over_climate_valve_mono(hass: HomeAssistant, skip_hass_states_get
         mock_service_call.assert_has_calls(
             [
                 call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree'}),
-                call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree'}),
+                call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree'}),
                 # 6 = 18 (room) - 15 (current of underlying) + 3 (current offset)
                 call(domain='number', service='set_value', service_data={'value': 9.0}, target={'entity_id': 'number.mock_offset_calibration'})
             ]
@@ -365,25 +365,13 @@ async def test_over_climate_valve_multi_presence(
     mock_get_state_side_effect = SideEffects(
         {
             # Valve 1 is open
-            "number.mock_opening_degree1": State(
-                "number.mock_opening_degree1", "10", {"min": 0, "max": 100}
-            ),
-            "number.mock_closing_degree1": State(
-                "number.mock_closing_degree1", "90", {"min": 0, "max": 100}
-            ),
-            "number.mock_offset_calibration1": State(
-                "number.mock_offset_calibration1", "0", {"min": -12, "max": 12}
-            ),
+            "number.mock_opening_degree1": State("number.mock_opening_degree1", "10", {"min": 0, "max": 100}),
+            "number.mock_closing_degree1": State("number.mock_closing_degree1", "89", {"min": 0, "max": 100}),
+            "number.mock_offset_calibration1": State("number.mock_offset_calibration1", "0", {"min": -12, "max": 12}),
             # Valve 2 is closed
-            "number.mock_opening_degree2": State(
-                "number.mock_opening_degree2", "0", {"min": 0, "max": 100}
-            ),
-            "number.mock_closing_degree2": State(
-                "number.mock_closing_degree2", "100", {"min": 0, "max": 100}
-            ),
-            "number.mock_offset_calibration2": State(
-                "number.mock_offset_calibration2", "10", {"min": -12, "max": 12}
-            ),
+            "number.mock_opening_degree2": State("number.mock_opening_degree2", "0", {"min": 0, "max": 100}),
+            "number.mock_closing_degree2": State("number.mock_closing_degree2", "99", {"min": 0, "max": 100}),
+            "number.mock_offset_calibration2": State("number.mock_offset_calibration2", "10", {"min": -12, "max": 12}),
         },
         State("unknown.entity_id", "unknown"),
     )
@@ -443,10 +431,10 @@ async def test_over_climate_valve_multi_presence(
             call('climate', 'set_temperature', {'entity_id': 'climate.mock_climate1', 'temperature': 19.0}),
             call('climate', 'set_temperature', {'entity_id': 'climate.mock_climate2', 'temperature': 19.0}),
             call(domain='number', service='set_value', service_data={'value': 40}, target={'entity_id': 'number.mock_opening_degree1'}),
-            call(domain='number', service='set_value', service_data={'value': 60}, target={'entity_id': 'number.mock_closing_degree1'}),
+            call(domain='number', service='set_value', service_data={'value': 59}, target={'entity_id': 'number.mock_closing_degree1'}),
             call(domain='number', service='set_value', service_data={'value': 3.0}, target={'entity_id': 'number.mock_offset_calibration1'}),
             call(domain='number', service='set_value', service_data={'value': 40}, target={'entity_id': 'number.mock_opening_degree2'}),
-            call(domain='number', service='set_value', service_data={'value': 60}, target={'entity_id': 'number.mock_closing_degree2'}),
+            call(domain='number', service='set_value', service_data={'value': 59}, target={'entity_id': 'number.mock_closing_degree2'}),
             call(domain='number', service='set_value', service_data={'value': 12}, target={'entity_id': 'number.mock_offset_calibration2'})
             ]
         )
@@ -474,10 +462,10 @@ async def test_over_climate_valve_multi_presence(
             call('climate', 'set_temperature', {'entity_id': 'climate.mock_climate1', 'temperature': 17.2}),
             call('climate', 'set_temperature', {'entity_id': 'climate.mock_climate2', 'temperature': 17.2}),
             call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree1'}),
-            call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree1'}),
+            call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree1'}),
             call(domain='number', service='set_value', service_data={'value': 3.0}, target={'entity_id': 'number.mock_offset_calibration1'}),
             call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree2'}),
-            call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree2'}),
+            call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree2'}),
             call(domain='number', service='set_value', service_data={'value': 12}, target={'entity_id': 'number.mock_offset_calibration2'})
             ]
         )
@@ -628,10 +616,10 @@ async def test_over_climate_valve_multi_min_opening_degrees(
         mock_service_call.assert_has_calls([
             # min is 60
             call(domain='number', service='set_value', service_data={'value': 68}, target={'entity_id': 'number.mock_opening_degree1'}),
-            call(domain='number', service='set_value', service_data={'value': 32}, target={'entity_id': 'number.mock_closing_degree1'}),
+            call(domain='number', service='set_value', service_data={'value': 31}, target={'entity_id': 'number.mock_closing_degree1'}),
             call(domain='number', service='set_value', service_data={'value': 3.0}, target={'entity_id': 'number.mock_offset_calibration1'}),
             call(domain='number', service='set_value', service_data={'value': 76}, target={'entity_id': 'number.mock_opening_degree2'}),
-            call(domain='number', service='set_value', service_data={'value': 24}, target={'entity_id': 'number.mock_closing_degree2'}),
+            call(domain='number', service='set_value', service_data={'value': 23}, target={'entity_id': 'number.mock_closing_degree2'}),
             call(domain='number', service='set_value', service_data={'value': 12}, target={'entity_id': 'number.mock_offset_calibration2'})
             ]
         )
@@ -657,10 +645,10 @@ async def test_over_climate_valve_multi_min_opening_degrees(
         assert mock_service_call.call_count == 6
         mock_service_call.assert_has_calls([
             call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree1'}),
-            call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree1'}),
+            call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree1'}),
             call(domain='number', service='set_value', service_data={'value': 7.0}, target={'entity_id': 'number.mock_offset_calibration1'}),
             call(domain='number', service='set_value', service_data={'value': 0}, target={'entity_id': 'number.mock_opening_degree2'}),
-            call(domain='number', service='set_value', service_data={'value': 100}, target={'entity_id': 'number.mock_closing_degree2'}),
+            call(domain='number', service='set_value', service_data={'value': 99}, target={'entity_id': 'number.mock_closing_degree2'}),
             call(domain='number', service='set_value', service_data={'value': 12}, target={'entity_id': 'number.mock_offset_calibration2'})
             ]
         )