diff --git a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
index bc7d5961..38bf18a3 100644
--- a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
+++ b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
@@ -678,26 +678,22 @@ def test_api_0380_heat_pump_no_pumps_fans_kwh_per_table_4f() -> None:
     assert result.pumps_fans_kwh_per_yr == 0.0
 
 
-def test_api_0380_mean_internal_temp_matches_worksheet_92_within_1e_2() -> None:
+def test_api_0380_mean_internal_temp_matches_worksheet_92_within_1e_3() -> None:
     # Arrange — SAP 10.2 Appendix N3.5 (PDF p.107) replaces Table 9c
     # steps 3-4 for heat-pump packages with PCDB data: each month
-    # blends Th, T_unimodal, T_bimodal via Equation N5, where N24,9_m
-    # and N16,9_m come from Table N5 (PSR-interpolated) and the day
-    # allocation algorithm.
+    # blends Th, T_unimodal, T_bimodal via Equation N5.
     #
     # Cert 0380 (Mitsubishi PUZ-WM50VHA, PCDB 104568, PSR ≈ 1.43)
     # lands on Table N5 row "1.2 or more" → annual totals (3, 38) →
-    # Jan(3, 28) + Dec(0, 10) extended days. Pre-fix the cascade ran
-    # pure-bimodal so Jan = 17.85 vs worksheet (92) Jan = 18.95
-    # (Δ -1.10) and Dec = 17.85 vs worksheet 18.16 (Δ -0.31).
+    # Jan(3, 28) + Dec(0, 10) extended days.
     #
-    # Tolerance 1e-2 absorbs a separate cold-month residual of +0.008°C
-    # caused by `internal_gains_from_cert` injecting the central-heating
-    # pump's gain (~7 W heating-season) for HP certs even though SAP 10.2
-    # Table 4f says HP packages contribute zero pump/fan gains (line 70
-    # of cert 0380's worksheet is 0.0 for every month). That residual
-    # is the §5-gating concern of the next slice; this slice's contract
-    # is the §7 N3.5 extended-heating cascade alone.
+    # Pre-slice-102f-prep.6 the cold-month MIT drifted +0.008°C due to
+    # `internal_gains_from_cert` injecting the central-heating pump's
+    # heating-season gain (~7 W) on HP certs. SAP 10.2 Table 4f
+    # specifies zero pump/fan gains on HP packages (cert 0380's
+    # worksheet line 70 = 0.0 every month) — that gating drops the
+    # spurious gain and tightens the MIT cascade against worksheet
+    # (92) to 1e-3 per month.
     doc = json.loads(_API_0380_JSON.read_text())
     epc = EpcPropertyDataMapper.from_api_response(doc)
 
@@ -712,7 +708,7 @@ def test_api_0380_mean_internal_temp_matches_worksheet_92_within_1e_2() -> None:
     for m, (cascade, ws) in enumerate(zip(
         inputs.mean_internal_temp_monthly_c, worksheet_mit_92
     )):
-        assert abs(cascade - ws) < 1e-2, (
+        assert abs(cascade - ws) < 1e-3, (
             f"month {m + 1}: cascade={cascade:.4f} vs worksheet={ws:.4f}"
         )
 
diff --git a/domain/sap10_calculator/worksheet/internal_gains.py b/domain/sap10_calculator/worksheet/internal_gains.py
index 2f6771a0..90071b1c 100644
--- a/domain/sap10_calculator/worksheet/internal_gains.py
+++ b/domain/sap10_calculator/worksheet/internal_gains.py
@@ -615,6 +615,22 @@ def _pump_date_category_from_cert(epc: EpcPropertyData) -> PumpDateCategory:
     return PumpDateCategory.UNKNOWN
 
 
+# SAP 10.2 Table 4f categories that do NOT apply a central-heating pump
+# gain in §5: the pump/fan electricity is already accounted for in the
+# system COP / efficiency. Cert 0380's worksheet line (70) is 0.0 for
+# every month, confirming category 4 (heat pumps).
+_CATEGORIES_WITHOUT_CENTRAL_HEATING_PUMP: Final[frozenset[int]] = frozenset({4})
+
+
+def _main_heating_category_from_cert(epc: EpcPropertyData) -> Optional[int]:
+    """First main-heating detail's category, or None when the cert
+    lodges no main heating."""
+    details = epc.sap_heating.main_heating_details
+    if not details:
+        return None
+    return details[0].main_heating_category
+
+
 def internal_gains_from_cert(
     *,
     epc: EpcPropertyData,
@@ -668,9 +684,18 @@ def internal_gains_from_cert(
         daylight_factor=c_daylight,
     )
 
-    pump_w = central_heating_pump_w(
-        date_category=_pump_date_category_from_cert(epc)
-    )
+    # SAP 10.2 Table 4f: heat-pump packages (category 4) account for the
+    # circulation pump's electricity inside the system COP, so worksheet
+    # line (70) "Pumps, fans" is 0 for HP certs (cert 0380's worksheet
+    # confirms 0 every month). Bypass the pump-W computation rather than
+    # carrying it through `pumps_fans_monthly_w`'s seasonal mask.
+    main_category = _main_heating_category_from_cert(epc)
+    if main_category in _CATEGORIES_WITHOUT_CENTRAL_HEATING_PUMP:
+        pump_w = 0.0
+    else:
+        pump_w = central_heating_pump_w(
+            date_category=_pump_date_category_from_cert(epc)
+        )
     # Liquid-fuel + warm-air + PIV + MV + HIU branches default to zero for
     # the combi-gas-natural-vent population; future slices will detect them
     # from epc.main_heating_details + epc.mechanical_ventilation.