diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 29730560..71367992 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -794,6 +794,14 @@ _SECONDARY_HEATING_FRACTION_BY_CATEGORY: Final[dict[int, float]] = {
     5: 0.10,
     6: 0.10,
     7: 0.15,
+    8: 0.10,   # Electric underfloor heating (direct-acting electric, e.g.
+               # SAP code 424): SAP 10.2 Table 11 (PDF p.188) row
+               # "Integrated storage/direct-acting electric systems" /
+               # "Other electric systems" = 0.10. First exercised when the
+               # description-lodged-secondary fix routed cat-8 mains (which
+               # previously short-circuited to 0) through the Table 11
+               # lookup (cert 2051-9502, electric underfloor + assumed
+               # portable-electric secondary).
     9: 0.10,   # Warm-air systems (NOT heat pump): a gas/oil warm-air unit
                # is an "All gas, liquid and solid fuel systems" row (0.10),
                # and electric warm air is "Other electric systems" (also
@@ -2305,7 +2313,9 @@ def _hot_water_fuel_cost_gbp_per_kwh(
 
 
 def _secondary_fraction(
-    main: Optional[MainHeatingDetail], secondary_heating_type: object
+    main: Optional[MainHeatingDetail],
+    secondary_heating_type: object,
+    secondary_lodged: bool = False,
 ) -> float:
     """SAP 10.2 Table 11 lookup by main heating category, applied only
     when (a) the cert has a secondary system lodged OR (b) the main
@@ -2313,6 +2323,17 @@ def _secondary_fraction(
     heaters). Returns 0.0 when neither applies — the most common case
     for gas/oil main systems whose cert doesn't lodge a secondary.
 
+    `secondary_lodged` covers the gov-API path: the register publishes
+    the secondary as a DESCRIPTION (`secondary_heating.description`, e.g.
+    "Portable electric heaters (assumed)") even when the integer
+    `secondary_heating_type` code is absent. The description is
+    authoritative — a lodged secondary description means RdSAP assessed a
+    secondary (per §A.2.2 the assumed system is portable electric heaters)
+    and its Table 11 fraction must be costed. Without this a gas/oil
+    boiler main with an assumed portable-electric secondary dropped the
+    secondary entirely (sec_kWh=0), under-costing the dwelling and
+    over-rating its SAP by a clean systematic +2.7 (median).
+
     `main_heating_fraction` on the cert is NOT consulted here: empirical
     probe shows it tracks main-system-1 vs main-system-2 allocation in
     multi-main configurations (99% of corpus has =1, meaning "single
@@ -2334,7 +2355,7 @@ def _secondary_fraction(
     if main is None:
         return 0.0
     code = main.sap_main_heating_code
-    has_lodged_secondary = secondary_heating_type is not None
+    has_lodged_secondary = secondary_heating_type is not None or secondary_lodged
     force = code is not None and code in _FORCE_SECONDARY_FOR_MAIN_CODES
     if not has_lodged_secondary and not force:
         return 0.0
@@ -2346,6 +2367,19 @@ def _secondary_fraction(
     return _secondary_heating_fraction_for_category(main.main_heating_category)
 
 
+def _has_lodged_secondary_description(epc: EpcPropertyData) -> bool:
+    """True when the cert lodges a secondary-heating DESCRIPTION (the
+    gov-API path surfaces the secondary as `secondary_heating.description`,
+    e.g. "Portable electric heaters (assumed)", even when the integer
+    `secondary_heating_type` code is None). RdSAP treats a lodged
+    secondary as costed (§A.2.2), so this gates the Table 11 fraction."""
+    sec = epc.secondary_heating
+    if sec is None:
+        return False
+    desc = getattr(sec, "description", None)
+    return desc is not None and desc not in ("None", "")
+
+
 def _secondary_heating_fraction_for_category(
     main_heating_category: Optional[int],
 ) -> float:
@@ -4290,7 +4324,9 @@ def energy_requirements_section_from_cert(
     main_category = main.main_heating_category if main is not None else None
     main_fuel = _main_fuel_code(main)
     secondary_fraction_value = _secondary_fraction(
-        main, epc.sap_heating.secondary_heating_type if epc.sap_heating else None
+        main,
+        epc.sap_heating.secondary_heating_type if epc.sap_heating else None,
+        secondary_lodged=_has_lodged_secondary_description(epc),
     )
     # When no secondary system is lodged the worksheet displays (208) = 0;
     # the per-system fuel formula already collapses to 0 via fraction_201 = 0
@@ -6559,7 +6595,9 @@ def cert_to_inputs(
     # without recomputing it. Pure function over the cert; same value
     # later when §9a `space_heating_fuel_monthly_kwh` runs.
     secondary_fraction_value = _secondary_fraction(
-        main, epc.sap_heating.secondary_heating_type
+        main,
+        epc.sap_heating.secondary_heating_type,
+        secondary_lodged=_has_lodged_secondary_description(epc),
     )
     # SAP10.2 §4 — compute the worksheet (45..65) values now (they only
     # depend on the cert dwelling shape, not on water_efficiency). The
diff --git a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
index a00fca28..d0f12b4d 100644
--- a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
+++ b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
@@ -522,6 +522,27 @@ def test_main_heating_fraction_does_not_override_table11_secondary_default() ->
     assert inputs.secondary_heating_fraction == pytest.approx(0.1, abs=0.001)
 
 
+def test_secondary_fraction_fires_when_secondary_lodged_via_description_only() -> None:
+    # Arrange — SAP 10.2 Table 11 / RdSAP §A.2.2: a gas boiler main (cat 2,
+    # not in the §A.2.2 forced-secondary set) whose cert lodges NO integer
+    # `secondary_heating_type` but DOES carry a secondary DESCRIPTION (the
+    # gov-API path surfaces the secondary only as a description, e.g.
+    # "Portable electric heaters (assumed)") must cost the secondary at its
+    # Table 11 0.10 fraction. Previously this returned 0.0 — the secondary
+    # was dropped (sec_kWh=0) → a clean systematic SAP over-rate (+2.7 med).
+    from domain.sap10_calculator.rdsap.cert_to_inputs import _secondary_fraction  # pyright: ignore[reportPrivateUsage]
+
+    main = _gas_boiler_detail()  # cat 2, code 102 — not forced-secondary
+
+    # Act
+    no_secondary = _secondary_fraction(main, None, secondary_lodged=False)
+    description_lodged = _secondary_fraction(main, None, secondary_lodged=True)
+
+    # Assert — a description-only lodged secondary fires the 0.10 fraction.
+    assert no_secondary == 0.0
+    assert abs(description_lodged - 0.10) <= 1e-9
+
+
 def test_main_heating_fraction_missing_falls_back_to_table11_default() -> None:
     # Arrange — when main_heating_fraction isn't lodged AND the cert
     # has a secondary system lodged, Table 11's 0.10 default still