diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index db29fa0a..68c91620 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -5924,6 +5924,27 @@ def cert_to_inputs(
             has_balanced_mv=_has_balanced_mechanical_ventilation(epc),
         )
     )
+    # SAP 10.2 Table 4f note c) (PDF p.175): "Where there are two main
+    # heating systems include two figures from this table." A genuine
+    # second SPACE-heating main therefore contributes its own circulation
+    # pump alongside Main 1's. The "second main heating system" test is the
+    # same one §9a uses to split space-heating demand: a lodged
+    # `main_heating_fraction > 0`. This excludes DHW-only second mains
+    # (e.g. cert 000565 Main 2 = gas combi via WHC 914, fraction 0 — water
+    # heating only, no space-heating circulation pump). Simulated case 6
+    # (dual oil boiler, 51% rads + 49% underfloor) lodges Main 1 "2013 or
+    # later" (41 kWh) + Main 2 unknown-date (115 kWh) → worksheet (230c)
+    # central-heating pump = 41 + 115 = 156. The Main 2 oil-boiler aux
+    # (230d) is already summed in `_table_4f_additive_components`; this
+    # adds only the circulation pump.
+    _pumps_main_details = (
+        epc.sap_heating.main_heating_details if epc.sap_heating else []
+    )
+    if len(_pumps_main_details) >= 2:
+        _pumps_main_2 = _pumps_main_details[1]
+        _pumps_main_2_fraction = _pumps_main_2.main_heating_fraction
+        if _pumps_main_2_fraction is not None and _pumps_main_2_fraction > 0:
+            pumps_fans_kwh += _table_4f_circulation_pump_kwh(_pumps_main_2)
     pumps_fans_kwh += _table_4f_additive_components(epc)
     # Track the MEV/MVHR-fan portion separately so the cost cascade can
     # apply Table 12a Grid 2 `FANS_FOR_MECH_VENT` (0.58 high-frac on
diff --git a/tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py b/tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py
index 03f5fe93..847e7d0d 100644
--- a/tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py
+++ b/tests/domain/sap10_calculator/rdsap/test_golden_fixtures.py
@@ -82,9 +82,9 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
     _GoldenExpectation(
         cert_number="0240-0200-5706-2365-8010",
         actual_sap=73,
-        expected_sap_resid=+0,
-        expected_pe_resid_kwh_per_m2=+1.9459,
-        expected_co2_resid_tonnes_per_yr=+0.1226,
+        expected_sap_resid=-1,
+        expected_pe_resid_kwh_per_m2=+2.8092,
+        expected_co2_resid_tonnes_per_yr=+0.1385,
         notes=(
             "Detached house, TFA 118, age J, oil boiler PCDB-listed + PV + "
             "RR on BP[0]. Mapper DOES extract sap_room_in_roof.room_in_roof_"
@@ -136,7 +136,25 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "45°-inclined solar gains. Validated against the simulated-"
             "case-6 worksheet ((27a) U_eff 2.1062). The inclined solar "
             "gain dominates → SAP cont 72.14 → 72.55 (resid -1 → +0 "
-            "EXACT), PE +3.9138 → +1.9459, CO2 +0.2213 → +0.1226."
+            "EXACT), PE +3.9138 → +1.9459, CO2 +0.2213 → +0.1226. "
+            "Slice S0380.201 added the SECOND main heating system's "
+            "circulation pump per SAP 10.2 Table 4f note c) (PDF p.175) "
+            "\"Where there are two main heating systems include two "
+            "figures from this table\" — gated on a lodged "
+            "main_heating_fraction > 0 (a genuine second SPACE-heating "
+            "main, excluding DHW-only second mains). This cert is dual-"
+            "main oil combi 51%/49%; Main 2 pump_age unknown (115 kWh) "
+            "joins Main 1's 115 → cascade pumps_fans 315 → 430 (+115 "
+            "kWh/yr). The fix was validated against the simulated-case-6 "
+            "worksheet, whose (231) = 356 decomposes as (230c) central-"
+            "heating pump 156 (= Main 1 41 + Main 2 115) + (230d) oil "
+            "boiler pump 200 — proving the two-pump treatment is spec-"
+            "correct. Cascade SAP cont 72.55 → 72.18 (integer 73 → 72, "
+            "resid +0 → -1), PE +1.9459 → +2.8092, CO2 +0.1226 → "
+            "+0.1385. The lodged 73 carries Elmhurst's own rounding/"
+            "residual (this cert is API-only with no worksheet); the "
+            "worksheet-backed case 6 is the spec authority for the "
+            "archetype per [[feedback-worksheet-not-api-reference]]."
         ),
     ),
     _GoldenExpectation(
diff --git a/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py
index 94b6d7e8..57a07537 100644
--- a/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py
+++ b/tests/domain/sap10_calculator/worksheet/_elmhurst_worksheet_001431_case6.py
@@ -69,6 +69,14 @@ LINE_27_WINDOWS_W_PER_K: Final[float] = 22.7408
 LINE_27A_ROOF_WINDOWS_W_PER_K: Final[float] = 13.0375
 LINE_31_TOTAL_EXTERNAL_AREA_M2: Final[float] = 336.13
 
+# Worksheet (231) "Total electricity for the above, kWh/year" (Block 1).
+# Decomposes as (230c) central heating pump 156 + (230d) oil boiler pump
+# 200. (230c) = 41 (Main 1 circ pump, "2013 or later") + 115 (Main 2 circ
+# pump, unknown date) — the two-main-system circulation-pump pair per
+# SAP 10.2 Table 4f note c. (230d) = 2 × 100 oil-boiler aux (already
+# wired in `_table_4f_additive_components`).
+LINE_231_PUMPS_FANS_KWH: Final[float] = 356.0
+
 
 def _summary_pdf_to_textract_style_pages(pdf_path: Path) -> list[str]:
     """Convert a Summary PDF into the per-page text format the
diff --git a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
index 396247f6..c8db9ec1 100644
--- a/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
+++ b/tests/domain/sap10_calculator/worksheet/test_section_cascade_pins.py
@@ -278,6 +278,31 @@ def test_section_3_roof_windows_case6_match_pdf() -> None:
     )
 
 
+def test_section_4f_pumps_fans_case6_match_pdf() -> None:
+    """(231) pumps/fans pin for simulated case 6 — a DUAL-oil-boiler
+    detached dwelling. Worksheet (231) = 356 = (230c) central heating
+    pump 156 + (230d) oil boiler pump 200. (230c) is itself the two-
+    main-system circulation-pump pair per SAP 10.2 Table 4f note c
+    ("Where there are two main heating systems include two figures from
+    this table"): Main 1 41 kWh (pump age "2013 or later") + Main 2 115
+    kWh (pump age unknown). The pre-S0380.201 cascade summed only Main 1's
+    circulation pump (41) and gave (231) = 241."""
+    from domain.sap10_calculator.calculator import calculate_sap_from_inputs
+
+    # Arrange
+    epc = _w001431_case6.build_epc()
+
+    # Act
+    result = calculate_sap_from_inputs(cert_to_inputs(epc))
+
+    # Assert
+    _pin(
+        result.pumps_fans_kwh_per_yr,
+        _w001431_case6.LINE_231_PUMPS_FANS_KWH,
+        "§4f (231) case6",
+    )
+
+
 # ============================================================================
 # §4 Water heating — LINE_42..LINE_65 scalar + monthly tuples
 # ============================================================================