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 b376f876..fb5e8af8 100644
--- a/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
+++ b/backend/documents_parser/tests/test_summary_pdf_mapper_chain.py
@@ -202,6 +202,28 @@ def test_summary_001431_lpg_boiler_maps_main_fuel_to_bottled_lpg() -> None:
     assert epc.sap_heating.water_heating_fuel == 3
 
 
+def test_summary_001431_lpg_boiler_full_chain_sap_matches_worksheet_pdf() -> None:
+    # Arrange — the lpg-boiler "before" worksheet (P960-0001-001431):
+    # pre-1998 LPG boiler (SAP code 115, eff 61%) + 210 L cylinder, NO
+    # cylinder thermostat, control 2113 (room thermostat + TRVs, no
+    # programmer). RdSAP 10 §10.5 (p.57) "Hot water separately timed":
+    # a no-programmer + pre-1998 boiler is NOT separately timed, so the
+    # Table 2b temperature factor (53) is 0.78 (= 0.60 × 1.3), not
+    # 0.702 (× 0.9). Worksheet §11a lodges unrounded SAP -6.6499.
+    pages = _summary_pdf_to_textract_style_pages(_SUMMARY_001431_LPG_PDF)
+    site_notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(site_notes)
+
+    # Act
+    result = calculate_sap_from_inputs(
+        cert_to_inputs(epc, prices=SAP_10_2_SPEC_PRICES)
+    )
+
+    # Assert
+    worksheet_unrounded_sap = -6.6499
+    assert abs(result.sap_score_continuous - worksheet_unrounded_sap) < 1e-4
+
+
 def test_summary_001431_topfloor_flat_classified_as_top_floor() -> None:
     # Arrange — the recommendation "after" Summary lodges §6.0 "Position
     # of flat in block of flats: Top Floor": floor "A Another dwelling
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 395626d8..8a97cae0 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -5150,6 +5150,28 @@ _TABLE_4A_SOLID_FUEL_BOILER_CODES: Final[frozenset[int]] = frozenset(
 )
 
 
+# SAP 10.2 Table 4c(2) boiler controls (21xx) that carry NO programmer /
+# time switch: 2101 "No time or thermostatic control", 2103 "Room
+# thermostat only", 2111 "TRVs and bypass", 2113 "Room thermostat and
+# TRVs". Every other 21xx control includes a programmer (2102/2104/2105/
+# 2106 …) or time-and-temperature zone control (2110/2112). Used by the
+# RdSAP 10 §10.5 (PDF p.57) "Hot water separately timed" rule below.
+_BOILER_CONTROLS_WITHOUT_PROGRAMMER: Final[frozenset[int]] = frozenset(
+    {2101, 2103, 2111, 2113}
+)
+
+# SAP 10.2 Table 4b (PDF p.168) gas/LPG/biogas boilers lodged pre-1998
+# (fan-assisted flue 110-114 + balanced/open flue 115-119) plus the
+# pre-1998 liquid-fuel boilers (124 pre-1985, 125 1985-1997, 128 combi
+# pre-1998). Gas/LPG 101-109 and oil 126/127/129/130 are 1998-or-later.
+# Used by the RdSAP 10 §10.5 separate-timing rule: a 1998-or-later boiler
+# is always separately timed; a pre-1998 boiler only when a programmer
+# is present.
+_PRE_1998_BOILER_SAP_CODES: Final[frozenset[int]] = frozenset(
+    set(range(110, 120)) | {124, 125, 128}
+)
+
+
 def _separately_timed_dhw(
     epc: EpcPropertyData, main: Optional[MainHeatingDetail],
 ) -> bool:
@@ -5232,7 +5254,24 @@ def _separately_timed_dhw(
     # DHW is not separately timed.
     if epc.sap_heating.water_heating_code not in _WATER_INHERIT_FROM_MAIN_CODES:
         return False
-    return bool(epc.has_hot_water_cylinder)
+    if not epc.has_hot_water_cylinder:
+        return False
+    # RdSAP 10 §10.5 (PDF p.57) "Hot water separately timed":
+    #   No programmer, pre-1998 boiler → No
+    #   Programmer, pre-1998 boiler    → Yes
+    #   Post-1998 boiler               → Yes
+    # i.e. DHW is NOT separately timed only when a pre-1998 boiler is
+    # paired with a no-programmer control (Table 4c(2): room-thermostat-
+    # only / TRV-only). Every other boiler+cylinder cert keeps the
+    # separately-timed default — so the change is confined to old, low-
+    # control stock (this lpg-boiler "before" worksheet: code 115 + 2113
+    # → (53) temperature factor 0.78, not 0.702).
+    if (
+        main.main_heating_control in _BOILER_CONTROLS_WITHOUT_PROGRAMMER
+        and main.sap_main_heating_code in _PRE_1998_BOILER_SAP_CODES
+    ):
+        return False
+    return True
 
 
 def _table_2b_note_b_multiplier_applies(