diff --git a/tests/domain/modelling/test_products.py b/tests/domain/modelling/test_products.py
index e99daedc..1a97fb05 100644
--- a/tests/domain/modelling/test_products.py
+++ b/tests/domain/modelling/test_products.py
@@ -141,3 +141,30 @@ def test_heat_pump_rounds_design_heat_loss_up_to_the_next_band() -> None:
     assert abs(_pump_price(products, 15.0) - 10680.0) <= 1e-9
     assert abs(_pump_price(products, 15.01) - 11400.0) <= 1e-9  # above largest
     assert abs(_pump_price(products, 25.0) - 11400.0) <= 1e-9
+
+
+def _full_distribution(products: Products, radiator_count: int) -> float:
+    """Isolate the full distribution line: no-system (decommission 0) + pump
+    (4 kW) 9720 + cylinder 2382.60 = 12102.60 base."""
+    inputs = AshpCostInputs(
+        existing_system=AshpExistingSystem.NONE,
+        is_small_property=True,
+        design_heat_loss_kw=4.0,
+        radiator_count=radiator_count,
+        has_reusable_wet_system=False,
+    )
+    return products.ashp_bundle_cost(inputs).total - 12102.60
+
+
+def test_radiator_count_is_clamped_to_the_distribution_table_bounds() -> None:
+    # Arrange — the distribution table only spans 4-12 radiators, so a proxy
+    # count outside that range is clamped to the nearest band (ADR-0025).
+    products = Products()
+
+    # Act / Assert — below 4 prices as 4 (2220); above 12 prices as 12 (6288);
+    # in-range is exact.
+    assert abs(_full_distribution(products, 2) - 2220.0) <= 1e-9
+    assert abs(_full_distribution(products, 4) - 2220.0) <= 1e-9
+    assert abs(_full_distribution(products, 9) - 4680.0) <= 1e-9
+    assert abs(_full_distribution(products, 12) - 6288.0) <= 1e-9
+    assert abs(_full_distribution(products, 15) - 6288.0) <= 1e-9