diff --git a/ashvale/estimation.py b/ashvale/estimation.py
index cded302..d205108 100644
--- a/ashvale/estimation.py
+++ b/ashvale/estimation.py
@@ -105,12 +105,28 @@ class KalmanCV:
         return {"q": self.q, "r": self.r, "x": self.x.tolist(),
                 "P": self.P.tolist(), "initialised": self.initialised}
 
+    def load_state(self, d: Dict) -> None:
+        """Restore the estimate only, leaving q and r as configured.
+
+        q and r are tuning, not something the filter learned. Taking them from
+        the state file pins whatever values were in force when it was written,
+        so editing them in config.yaml does nothing until someone thinks to
+        delete the state, and nobody thinks to delete the state. That cost a
+        retune here: the new q was deployed, the service restarted, and the
+        filters quietly carried on with the old one.
+
+        P may be inconsistent with a newly changed q. That is harmless: the
+        filter re-converges within a few hundred samples, which is far cheaper
+        than a tuning change that appears to work and does not.
+        """
+        self.x = np.array(d["x"], dtype=float)
+        self.P = np.array(d["P"], dtype=float)
+        self.initialised = bool(d["initialised"])
+
     @classmethod
     def from_dict(cls, d: Dict) -> "KalmanCV":
         kf = cls(q=d["q"], r=d["r"])
-        kf.x = np.array(d["x"], dtype=float)
-        kf.P = np.array(d["P"], dtype=float)
-        kf.initialised = bool(d["initialised"])
+        kf.load_state(d)
         return kf
 
 
@@ -321,7 +337,13 @@ class SignalTracker:
         # Absent from state files written before humidity compensation existed.
         if d.get("hum_compensator"):
             self.hum_compensator = HumidityCompensator.from_dict(d["hum_compensator"])
-        self.filters = {k: KalmanCV.from_dict(v) for k, v in d["filters"].items()}
+        # Deliberately not KalmanCV.from_dict here: that would restore the
+        # persisted q and r over the configured ones. Only the estimate is
+        # restored, and only for filters this build still has.
+        for name, saved in d.get("filters", {}).items():
+            kf = self.filters.get(name)
+            if kf is not None:
+                kf.load_state(saved)
         self.last_ts = d.get("last_ts")
 
 
diff --git a/tests/test_estimation.py b/tests/test_estimation.py
index b1079bc..ba40d8a 100644
--- a/tests/test_estimation.py
+++ b/tests/test_estimation.py
@@ -333,3 +333,34 @@ def test_kalman_rate_is_physical_in_a_still_room():
     assert np.median(settled) < 3.0, (
         f"median |rate| {np.median(settled):.1f} C/h in a room drifting 0.4 C/h")
     assert np.percentile(settled, 95) < 10.0
+
+
+def test_retuning_q_survives_a_reload():
+    """Tuning lives in config, not in the state file.
+
+    q and r were persisted and restored, so a retune deployed to a running
+    station did nothing: the service restarted and the filters carried on with
+    whatever tuning was in force when the state was last written. The symptom
+    is a config change that appears to work and does not, which is the worst
+    kind.
+    """
+    from ashvale.config import load_config
+    from ashvale.estimation import SignalTracker
+
+    cfg = load_config()
+    cfg.sensor.kalman_q_temp = 2.0e-6          # an old, badly tuned state file
+    old = SignalTracker(cfg)
+    for i in range(50):
+        old.step(1.7554e9 + i * 2.0, 24.0, 50.0, 1013.0, 43.0)
+    saved = old.to_dict()
+    assert saved["filters"]["temperature"]["q"] == 2.0e-6
+
+    cfg.sensor.kalman_q_temp = 1.0e-9          # the retune
+    fresh = SignalTracker(cfg)
+    fresh.load_dict(saved)
+    assert fresh.filters["temperature"].q == 1.0e-9, \
+        "the state file overrode the configured tuning"
+    # the estimate itself must still be carried across
+    assert fresh.filters["temperature"].initialised
+    assert fresh.filters["temperature"].x[0] == pytest.approx(
+        old.filters["temperature"].x[0])