diff --git a/custom_components/heating_mpc/coordinator.py b/custom_components/heating_mpc/coordinator.py
index 2f6b6d5..3447922 100644
--- a/custom_components/heating_mpc/coordinator.py
+++ b/custom_components/heating_mpc/coordinator.py
@@ -166,8 +166,9 @@ class HeatingMPCCoordinator(DataUpdateCoordinator[dict[str, Any]]):
         self._update_counts()
 
     def _update_counts(self) -> None:
-        self._on_samples = min(m.on_count for m in self.learners.values())
-        self._off_samples = min(m.off_count for m in self.learners.values())
+        # Without zones (all deleted in the UI) there is nothing to count.
+        self._on_samples = min((m.on_count for m in self.learners.values()), default=0)
+        self._off_samples = min((m.off_count for m in self.learners.values()), default=0)
 
     def _sensor_quality(self, entity_id: str, now: datetime, limit: float) -> dict:
         state = self.hass.states.get(entity_id)
@@ -241,9 +242,9 @@ class HeatingMPCCoordinator(DataUpdateCoordinator[dict[str, Any]]):
         status["sample_results_since_start"] = dict(self._sample_results)
         # Least trained room: mean of its three readiness requirements (100 = ready).
         status["learning_progress"] = round(100 * min(
-            (min(1.0, m.count / READY_SAMPLES) + min(1.0, m.on_count / READY_ON_SAMPLES)
-             + min(1.0, m.off_count / READY_OFF_SAMPLES)) / 3
-            for m in self.learners.values()), 1)
+            ((min(1.0, m.count / READY_SAMPLES) + min(1.0, m.on_count / READY_ON_SAMPLES)
+              + min(1.0, m.off_count / READY_OFF_SAMPLES)) / 3
+             for m in self.learners.values()), default=0.0), 1)
 
     def _extended_diagnostics(self, room: str) -> dict[str, Any]:
         model = self.extended.get(room)
@@ -432,7 +433,7 @@ class HeatingMPCCoordinator(DataUpdateCoordinator[dict[str, Any]]):
             "temperatures": {r: round(t, 3) for r, t in temps.items() if t is not None},
             "zone_names": {key: zone.name for key, zone in self.zones.items()},
             "on_samples": self._on_samples, "off_samples": self._off_samples,
-            "samples": min(learner.count for learner in self.learners.values()),
+            "samples": min((learner.count for learner in self.learners.values()), default=0),
             "mode": climate.state if climate else "unavailable",
             "weather": {k: v for k, v in weather.items() if v is not None},
             "weather_active_sources": {k: v for k, v in active_sources.items() if v},
@@ -486,6 +487,8 @@ class HeatingMPCCoordinator(DataUpdateCoordinator[dict[str, Any]]):
             self._evaluator.reset_window()
             status["forecast_accuracy"] = self._evaluator.summary(self.rooms)
             self._count_result(status, "waiting_for_inputs")
+            if not self.zones:
+                status["status"] = "no_zones"
             return status
 
         # A zone learns only across a poll pair where it was usable at both ends with
@@ -587,7 +590,7 @@ class HeatingMPCCoordinator(DataUpdateCoordinator[dict[str, Any]]):
             "reference_heat": heater_on,
             "on_samples": self._on_samples,
             "off_samples": self._off_samples,
-            "samples": min(learner.count for learner in self.learners.values()),
+            "samples": min((learner.count for learner in self.learners.values()), default=0),
             "models": {
                 room: {"name": self.zones[room].name,
                        "loss": round(model.theta[0], 6),
diff --git a/tests/ha/test_lifecycle.py b/tests/ha/test_lifecycle.py
index 3262ce4..28a05a7 100644
--- a/tests/ha/test_lifecycle.py
+++ b/tests/ha/test_lifecycle.py
@@ -290,3 +290,18 @@ async def test_learning_progress_and_last_sample_sensors(hass, entry, inputs, fr
     last = hass.states.get(last_id)
     assert last.state == "waiting_for_inputs"
     assert last.attributes["counts_since_start"] == {"first_sample": 1, "learned": 1, "waiting_for_inputs": 1}
+
+
+async def test_deleting_the_last_zone_keeps_the_entry_loaded(hass, entry, inputs, caplog):
+    await setup(hass, entry)
+    assert hass.config_entries.async_remove_subentry(entry, zone_subentry(entry, "sensor.room").subentry_id)
+    await hass.async_block_till_done()
+    assert entry.state.name == "LOADED"
+    coordinator = hass.data[DOMAIN][entry.entry_id]
+    assert (coordinator.rooms, coordinator.data["status"]) == ([], "no_zones")
+    assert coordinator.data["learning_progress"] == 0
+    assert "Error setting up entry" not in caplog.text
+    # Adding a zone back resumes normally.
+    add_zone(hass, entry, "sensor.room", ["sensor.room"])
+    await hass.async_block_till_done()
+    assert hass.data[DOMAIN][entry.entry_id].data["status"] == "learning"