Elmhurst 'No Insulation' cylinder (0 mm lodged) takes the uninsulated storage loss 🟥

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py

@@ -6451,6 +6451,78 @@ def test_uninsulated_cylinder_computes_storage_loss_via_table2_jacket_t0() -> No
     assert got_jan_kwh > jacket_50mm_jan_kwh
 
 
+def test_elmhurst_no_insulation_cylinder_thickness_zero_takes_uninsulated_loss() -> None:
+    """The Elmhurst site-notes mapper lodges a "No Insulation" cylinder as
+    `cylinder_insulation_type=None` + `cylinder_insulation_thickness_mm=0`
+    — per its own comment "the lodged §15.1 Insulation Thickness (0 mm)
+    carries the storage-loss signal the cascade's SAP 10.2 Table 2
+    dispatch needs" (`_ELMHURST_CYLINDER_NO_INSULATION_LABELS`,
+    datatypes/epc/domain/mapper.py). The cascade must honour that signal:
+    a lodged 0 mm with no insulation type is the uninsulated cylinder —
+    Table 2 loose-jacket branch at t = 0 — not the zero-loss combi
+    default it previously fell to (the type-None guard returned None
+    before the thickness was ever read).
+    """
+    # Arrange — same dwelling as the type-0 test; only the lodgement
+    # shape differs (type None + explicit 0 mm, the Elmhurst path).
+    from domain.sap10_calculator.worksheet.water_heating import (
+        cylinder_storage_loss_factor_table_2,
+        cylinder_temperature_factor_table_2b,
+        cylinder_volume_factor_table_2a,
+    )
+
+    hp_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=29,
+        heat_emitter_type=1,
+        emitter_temperature=1,
+        main_heating_control=2206,
+        main_heating_category=4,
+        sap_main_heating_code=None,
+    )
+    epc = make_minimal_sap10_epc(
+        total_floor_area_m2=_TYPICAL_TFA_M2,
+        habitable_rooms_count=4,
+        country_code="ENG",
+        has_hot_water_cylinder=True,
+        sap_building_parts=[make_building_part()],
+        sap_heating=make_sap_heating(
+            main_heating_details=[hp_main],
+            water_heating_code=901,
+            cylinder_size=3,  # Medium → 160 L
+            cylinder_insulation_type=None,  # Elmhurst "No Insulation"
+            cylinder_insulation_thickness_mm=0,
+            cylinder_thermostat="Y",
+        ),
+    )
+    expected_jan_kwh = (
+        160.0
+        * cylinder_storage_loss_factor_table_2(
+            insulation_type="loose_jacket", thickness_mm=0.0
+        )
+        * cylinder_volume_factor_table_2a(160.0)
+        * cylinder_temperature_factor_table_2b(
+            has_cylinder_thermostat=True, separately_timed_dhw=True
+        )
+        * 31
+    )
+
+    # Act
+    wh_result, _ = _water_heating_worksheet_and_gains(
+        epc=epc,
+        water_efficiency_pct=1.7,
+        is_instantaneous=False,
+        primary_age="D",
+        pcdb_record=None,
+    )
+
+    # Assert — identical series to the gov-API type-0 lodgement: the two
+    # front-ends describe the same uninsulated cylinder.
+    assert wh_result is not None
+    got_jan_kwh = wh_result.solar_storage_monthly_kwh[0]
+    assert abs(got_jan_kwh - expected_jan_kwh) < 1e-4
+
+
 def test_no_water_heating_default_age_a_to_f_uses_12mm_loose_jacket_per_table_29() -> None:
     """RdSAP 10 §10.7 + Table 29 (PDF p.55-56): when no water heating
     system is lodged, the default cylinder takes the age-band insulation,