diff --git a/backend/documents_parser/tests/test_heating_systems_corpus.py b/backend/documents_parser/tests/test_heating_systems_corpus.py
index f008d0ee..6ec58ca7 100644
--- a/backend/documents_parser/tests/test_heating_systems_corpus.py
+++ b/backend/documents_parser/tests/test_heating_systems_corpus.py
@@ -716,11 +716,23 @@ _EXPECTATIONS: tuple[_CorpusExpectation, ...] = (
     # / cost −£12.16 is the heat-network cost/standing residual exposed
     # by S0380.175 (cost-side, untouched by this CO2/PE slice). CH3
     # unchanged (code 304 community-HP COP front).
+    #
+    # Slice S0380.183 closed the CH2/CH4 HW cost residual: per SAP 10.2
+    # §10b the community-heating HW bills at the heat-network rate, not
+    # the Elmhurst §15.0 "Mains gas" placeholder. Worksheet (342) =
+    # (310) × the S0380.171 CHP heat-fraction blend (= the same rate as
+    # space heating (340)), not (310) × 3.48 p/kWh gas. Extended
+    # `_is_community_heating_hw_from_main` to include code 302 — the
+    # S0380.182 CO2/PE interception sits above this predicate's branch,
+    # so it now affects only the cost path. CH2 + CH4 are FULLY EXACT
+    # on all four metrics. CH6 SAP −7.49→−8.02 / cost +£172.68→+£184.84
+    # (its HW now also bills the blend, compounding the DLF=1.0 quirk —
+    # same root, still the separate CH6 DLF front).
     _CorpusExpectation(variant='community heating 1', block='11b', expected_sap_resid=+0.0000, expected_cost_resid_gbp=-0.0000, expected_co2_resid_kg=-0.0000, expected_pe_resid_kwh=+0.0000),
-    _CorpusExpectation(variant='community heating 2', block='11b', expected_sap_resid=+0.5277, expected_cost_resid_gbp=-12.1598, expected_co2_resid_kg=+0.0000, expected_pe_resid_kwh=+0.0000),
+    _CorpusExpectation(variant='community heating 2', block='11b', expected_sap_resid=-0.0000, expected_cost_resid_gbp=-0.0000, expected_co2_resid_kg=+0.0000, expected_pe_resid_kwh=+0.0000),
     _CorpusExpectation(variant='community heating 3', block='11b', expected_sap_resid=+0.0000, expected_cost_resid_gbp=-0.0000, expected_co2_resid_kg=-75.3228, expected_pe_resid_kwh=-249.3161),
-    _CorpusExpectation(variant='community heating 4', block='11b', expected_sap_resid=+0.5277, expected_cost_resid_gbp=-12.1598, expected_co2_resid_kg=-0.0000, expected_pe_resid_kwh=-0.0000),
-    _CorpusExpectation(variant='community heating 6', block='11b', expected_sap_resid=-7.4942, expected_cost_resid_gbp=+172.6778, expected_co2_resid_kg=+2411.5399, expected_pe_resid_kwh=+5023.4766),
+    _CorpusExpectation(variant='community heating 4', block='11b', expected_sap_resid=-0.0000, expected_cost_resid_gbp=-0.0000, expected_co2_resid_kg=-0.0000, expected_pe_resid_kwh=-0.0000),
+    _CorpusExpectation(variant='community heating 6', block='11b', expected_sap_resid=-8.0219, expected_cost_resid_gbp=+184.8376, expected_co2_resid_kg=+2411.5399, expected_pe_resid_kwh=+5023.4766),
 )
 
 
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 7aa5ce36..2dd9fc04 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -1496,24 +1496,26 @@ def _water_heating_fuel_code(epc: EpcPropertyData) -> Optional[int]:
 
 def _is_community_heating_hw_from_main(epc: EpcPropertyData) -> bool:
     """True iff the cert's WHC routes HW from the main heating system
-    (codes 901 / 902 / 914) AND the main is a single-source heat
-    network with a registered heat-source efficiency
-    (`_HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY` — currently SAP code 301
-    boilers and 304 HP).
+    (codes 901 / 902 / 914) AND the main is a heat network the cascade
+    can cost/emission-rate: a registered single-source heat-source
+    efficiency (`_HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY` — SAP code 301
+    boilers / 304 HP) OR code 302 (CHP and boilers).
 
     Elmhurst Summary §15.0 lodges `water_heating_fuel_type = "Mains gas"`
     on community-heating certs regardless of the actual heat-network
     source — without this guard the HW cost / CO2 / PE bills via the
     Mains-gas Table 12 code (3.48 p/kWh / 0.21 / 1.13) instead of the
-    heat-network code (4.24 p/kWh / Table 12 code 41 / 51).
+    heat-network rate.
 
-    SAP code 302 (CHP+boilers) is excluded because the 35%/65% split
-    requires the displaced-electricity credit line per spec block 13b
-    (464)/(466) on the HW side — same constraint as `_main_heating_
-    co2_factor_kg_per_kwh` (S0380.172). Routing HW through main for
-    SAP 302 without the credit cascade would regress CO2 / PE; both
-    the SH and HW paths converge in a single follow-up slice that
-    wires the CHP credit + boiler-side factor split.
+    SAP code 302 (CHP+boilers) was previously excluded because the
+    35%/65% split needs the displaced-electricity credit line (spec
+    block 12b/13b (364)/(366)/(464)/(466)). S0380.182 wired that credit
+    via `_heat_network_code_302_effective_factor`, which intercepts the
+    HW CO2/PE helpers ABOVE this predicate's branch — so including 302
+    here now affects only the COST path, routing HW cost through
+    `_fuel_cost_gbp_per_kwh(main)` = the S0380.171 CHP heat-fraction
+    blend (the same rate as space heating, worksheet (342) = (310) ×
+    blend). Closes the CH2/CH4 HW cost residual (S0380.183).
     """
     if epc.sap_heating.water_heating_code not in _WATER_INHERIT_FROM_MAIN_CODES:
         return False
@@ -1521,7 +1523,10 @@ def _is_community_heating_hw_from_main(epc: EpcPropertyData) -> bool:
     if not _is_heat_network_main(main):
         return False
     code = main.sap_main_heating_code if main is not None else None
-    return isinstance(code, int) and code in _HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY
+    return isinstance(code, int) and (
+        code in _HEAT_NETWORK_HEAT_SOURCE_EFFICIENCY
+        or code == _SAP_CODE_COMMUNITY_CHP_AND_BOILERS
+    )
 
 
 def _main_heating_efficiency(epc: EpcPropertyData) -> float: