diff --git a/datatypes/epc/domain/mapper.py b/datatypes/epc/domain/mapper.py
index c36f3ef8c..1985db439 100644
--- a/datatypes/epc/domain/mapper.py
+++ b/datatypes/epc/domain/mapper.py
@@ -6128,7 +6128,10 @@ def _map_sap_heating(
         secondary_heating_type=heating.secondary_heating.secondary_system,
         shower_outlets=shower_outlets,
         cylinder_size=(
-            heating.water_heating.cylinder_size
+            _pashub_cylinder_size_code(
+                heating.water_heating.cylinder_size,
+                heating.water_heating.system,
+            )
             if cylinder_present
             else None
         ),
@@ -6172,6 +6175,45 @@ def _pashub_mechanical_ventilation_kind(
     return _PASHUB_VENTILATION_TYPE_TO_KIND[ventilation_type]
 
 
+# PasHub surveyed §Water-Heating "Cylinder Size" band → SAP10 cylinder-size
+# enum (Table 28: 2=Normal/110L, 3=Medium/160L, 4=Large/210L). PasHub renders
+# the band with its own litre-range suffix (unlike the Elmhurst forms in
+# `_ELMHURST_CYLINDER_SIZE_LABEL_TO_SAP10`); the raw string was int-or-noned by
+# `_cylinder_volume_l_from_code`, silently skipping the Table 28 volume
+# convention (issue #1590 bug 6).
+_PASHUB_CYLINDER_SIZE_TO_SAP10: Dict[str, int] = {
+    "Normal (90-130 litres)": 2,
+    "Large (>170 litres)": 4,
+}
+
+
+def _pashub_cylinder_size_code(
+    size_label: Optional[str], system_label: str
+) -> Optional[int]:
+    """Resolve a PasHub surveyed Cylinder Size band to the SAP10 enum at the
+    mapper boundary (ADR-0015). "No Access" follows RdSAP 10 Table 28 (p.55):
+    off-peak dual electric immersion → 210 L, solid-fuel boiler → 160 L,
+    otherwise → 110 L (code 2) — the cohort's case is a cylinder fed from the
+    gas main. An electric-immersion "No Access" needs the meter-type context
+    this path doesn't yet plumb, so it strict-raises (loud gap, mirroring the
+    cohort-scoped control approach) rather than silently taking the 110 L
+    branch; any other uncovered non-empty label strict-raises too."""
+    if not size_label or size_label == "No Cylinder":
+        return None
+    if size_label == "No Access":
+        if system_label == "Electric immersion":
+            raise UnmappedPasHubLabel(
+                "cylinder size",
+                "'No Access' on an electric immersion needs meter-type "
+                "context (RdSAP 10 Table 28 210L branch) — not yet mapped",
+            )
+        return 2  # Table 28 "otherwise": 110 L
+    code = _PASHUB_CYLINDER_SIZE_TO_SAP10.get(size_label)
+    if code is None:
+        raise UnmappedPasHubLabel("cylinder size", size_label)
+    return code
+
+
 def _map_sap_ventilation(ventilation: Ventilation) -> SapVentilation:
     return SapVentilation(
         ventilation_type=ventilation.ventilation_type,
diff --git a/datatypes/epc/domain/tests/test_from_site_notes.py b/datatypes/epc/domain/tests/test_from_site_notes.py
index 77e99403c..844a17a03 100644
--- a/datatypes/epc/domain/tests/test_from_site_notes.py
+++ b/datatypes/epc/domain/tests/test_from_site_notes.py
@@ -1038,7 +1038,7 @@ class TestFromSiteNotesExample1:
                     )
                 ],
                 has_fixed_air_conditioning=False,
-                cylinder_size="Normal (90-130 litres)",
+                cylinder_size=2,  # "Normal (90-130 litres)" → Table 28 code 2
                 cylinder_insulation_type="Factory fitted",
                 cylinder_insulation_thickness_mm=12,
                 water_heating_code=901,  # cylinder + "From main heating 1" → WHC 901