diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index a2b988c9..6a4bfbba 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -2082,23 +2082,6 @@ def _off_peak_low_rate_gbp_per_kwh(tariff: Tariff) -> float:
     return low * _PENCE_TO_GBP
 
 
-def _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type: object) -> float:
-    """Off-peak low-rate £/kWh for callsites that detect off-peak via the
-    `_is_off_peak_meter` heuristic (RdSAP meter code 3 = Unknown is
-    treated as off-peak for electric end-uses; see _is_off_peak_meter
-    docstring). When the meter resolves to a known off-peak tariff
-    (codes 1/4/5), bills at that tariff's Table 32 low rate; when the
-    meter resolves to STANDARD (codes 2 = Single, 3 = Unknown), falls
-    back to the SEVEN_HOUR rate (5.50, Table 32 code 31). Codifies the
-    heuristic that pre-S0380.138 was baked into the literal
-    `prices.e7_low_rate_p_per_kwh` constant."""
-    tariff = tariff_from_meter_type(meter_type)
-    if tariff is Tariff.STANDARD:
-        _high, low = _tariff_high_low_rates_p_per_kwh(Tariff.SEVEN_HOUR)
-        return low * _PENCE_TO_GBP
-    return _off_peak_low_rate_gbp_per_kwh(tariff)
-
-
 # Tariff → (high_rate_fuel_code, low_rate_fuel_code) for the SAP 10.2
 # Table 12d (CO2) / Table 12e (PE) monthly factors. Mirror of the
 # Table 32 cost-rates dict above: 7-hour and 10-hour tariffs split into
@@ -2660,30 +2643,25 @@ def _pv_export_credit_gbp_per_kwh() -> float:
 
 
 def _pv_dwelling_import_price_gbp_per_kwh(
-    meter_type: object, prices: PriceTable
+    tariff: Tariff, prices: PriceTable
 ) -> float:
     """PV dwelling-consumption price per kWh per SAP 10.2 Appendix M1 §6
-    (p.94): "apply the normal import electricity price to PV energy used
-    within the dwelling". Onsite-consumed PV displaces grid IMPORTS, so
-    it bills at the standard electricity import tariff (Table 32 code 30
-    under the RdSAP10 amendment per ADR-0010 §10 = 13.19 p/kWh — the
-    same rate `_fuel_cost`'s `other_uses_p_per_kwh` already pays for
-    lighting/pumps/fans, and crucially the same rate Table 32 code 60
-    pays for the EXPORT credit. In Table 32 these collapse to a single
-    13.19 p value, so the IMPORT/EXPORT split is mathematically
-    equivalent to the legacy single-rate-EXPORT credit — but the
-    distinction matters when an off-peak tariff lands: §6 then directs
-    a weighted Table 12a high/low rate, deferred until the first off-
-    peak cost cert ships."""
-    if _is_off_peak_meter(meter_type, fuel_is_electric=True):
-        # Off-peak weighted Table 12a rate (deferred — `_fuel_cost`
-        # short-circuits Tariff != STANDARD before reaching this path).
-        # Routes through the meter-heuristic helper so an Unknown-meter
-        # cert (code 3 = "treat as off-peak for electric end-uses" per
-        # _is_off_peak_meter) falls back to the SEVEN_HOUR low rate
-        # rather than raising on STANDARD.
-        return _off_peak_low_rate_gbp_per_kwh_via_meter_heuristic(meter_type)
-    return table_32_unit_price_p_per_kwh(30) * _PENCE_TO_GBP
+    (PDF p.94, lines 5510-5513): "apply the normal import electricity
+    price to PV energy used within the dwelling … In the case of the
+    former, use a weighted average of high and low rates (Table 12a)."
+
+    Onsite-consumed PV displaces the dwelling's "all other uses"
+    electricity (lighting / appliances / pumps), so it bills at the same
+    Table 12a Grid 2 ALL_OTHER_USES rate `_other_fuel_cost_gbp_per_kwh`
+    derives — a STANDARD-tariff dwelling pays the flat Table 32 code 30
+    13.19 p/kWh (unchanged from the legacy single-rate path), while an
+    off-peak dwelling pays the weighted high/low blend (7-hour:
+    0.90 × 15.29 + 0.10 × 5.50 = 14.311 p/kWh, matching worksheet
+    (252)/(269) "PV used in dwelling" on case 19).
+
+    Pre-S0380.233 the off-peak branch returned the bare low rate
+    (5.50 p/kWh), under-crediting onsite PV on every off-peak cert."""
+    return _other_fuel_cost_gbp_per_kwh(tariff, prices)
 
 
 def _other_fuel_cost_gbp_per_kwh(
@@ -6137,9 +6115,7 @@ def _fuel_cost(
         pv_dwelling_kwh_per_yr=pv_dwelling_kwh_per_yr,
         pv_exported_kwh_per_yr=pv_exported_kwh_per_yr,
         pv_dwelling_import_price_gbp_per_kwh=(
-            _pv_dwelling_import_price_gbp_per_kwh(
-                epc.sap_energy_source.meter_type, prices
-            )
+            _pv_dwelling_import_price_gbp_per_kwh(_rdsap_tariff(epc), prices)
         ),
     )
 
@@ -6976,7 +6952,7 @@ def cert_to_inputs(
         pv_generation_kwh_per_yr=_pv_generation_kwh_per_yr(epc, climate),
         pv_export_credit_gbp_per_kwh=_pv_export_credit_gbp_per_kwh(),
         pv_dwelling_import_price_gbp_per_kwh=_pv_dwelling_import_price_gbp_per_kwh(
-            epc.sap_energy_source.meter_type, prices
+            _rdsap_tariff(epc), prices
         ),
         # SAP 10.2 Appendix M1 §3-4 PV split — the cascade applies
         # IMPORT PEF (Table 12) to the onsite portion and EXPORT PEF
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 bde4bb44..ad5b3553 100644
--- a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
+++ b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
@@ -61,6 +61,7 @@ from domain.sap10_calculator.rdsap.cert_to_inputs import (
     _main_floor_u_value,  # pyright: ignore[reportPrivateUsage]
     _main_space_heating_high_rate_fraction,  # pyright: ignore[reportPrivateUsage]
     _other_fuel_cost_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
+    _pv_dwelling_import_price_gbp_per_kwh,  # pyright: ignore[reportPrivateUsage]
     _pv_eligible_demand_monthly_kwh,  # pyright: ignore[reportPrivateUsage]
     _primary_loss_applies,  # pyright: ignore[reportPrivateUsage]
     _rdsap_extract_fans_default,  # pyright: ignore[reportPrivateUsage]
@@ -1852,6 +1853,28 @@ def test_pv_eligible_demand_excludes_low_rate_main_space_heating() -> None:
         assert abs(included[m] - (base[m] + secondary[m] + main_1[m])) <= 1e-9
 
 
+def test_pv_dwelling_import_price_blends_high_low_on_off_peak() -> None:
+    # Arrange — SAP 10.2 Appendix M1 §6 (PDF p.94, lines 5510-5513): PV
+    # used in the dwelling is credited at "a weighted average of high and
+    # low rates (Table 12a)". On a 7-hour tariff the ALL_OTHER_USES blend
+    # is 0.90 × 15.29 + 0.10 × 5.50 = 14.311 p/kWh (worksheet case 19
+    # (252) "PV used in dwelling" = 14.3110). STANDARD tariff has no
+    # split → flat Table 32 code 30 = 13.19 p/kWh (unchanged).
+    from domain.sap10_calculator.tables.table_12a import Tariff
+
+    # Act
+    off_peak = _pv_dwelling_import_price_gbp_per_kwh(
+        Tariff.SEVEN_HOUR, SAP_10_2_SPEC_PRICES
+    )
+    standard = _pv_dwelling_import_price_gbp_per_kwh(
+        Tariff.STANDARD, SAP_10_2_SPEC_PRICES
+    )
+
+    # Assert
+    assert abs(off_peak - 0.14311) <= 1e-6
+    assert abs(standard - 0.1319) <= 1e-6
+
+
 def test_is_off_peak_meter_recognises_bare_18_hour_lodging() -> None:
     # Arrange — RdSAP 10 §17 page 85 row 10-2 lodges 18-hour meter
     # as the bare "18-hour" or "18 Hour" form (Elmhurst Summary §14.2