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 fbdde3f29..762f7bb40 100644
--- a/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
+++ b/tests/domain/sap10_calculator/rdsap/test_cert_to_inputs.py
@@ -9189,6 +9189,45 @@ def test_water_only_heat_network_half_charge_reaches_the_fuel_cost_worksheet() -
     assert abs(fc.additional_standing_charges_gbp - 180.0) <= 1e-9
 
 
+def test_water_only_heat_network_half_charge_reaches_the_off_peak_standing_scalar() -> None:
+    # Arrange — cert 22032926 (22 Gwydyr Mansions) in shape: electric storage
+    # main (SAP 401) on a Dual meter + WHC 950. Off-peak certs take the zero
+    # `FuelCostResult` sentinel from `_fuel_cost` and cost via the scalar
+    # `standing_charges_gbp` instead, so the §C6 half must reach BOTH paths —
+    # this is the one the corpus cert actually bills through.
+    #
+    # The lodged `water_heating_fuel` 20 ("mains gas (community)") is NOT a
+    # Table 32 gas code, so note (a) draws no gas standing — the dwelling has
+    # no gas meter, only the Economy-7 electric one. Hence £24 today.
+    from dataclasses import replace
+
+    base = _typical_semi_detached_epc()
+    storage_main = MainHeatingDetail(
+        has_fghrs=False,
+        main_fuel_type=29,  # electricity
+        heat_emitter_type=0,
+        emitter_temperature=1,
+        main_heating_control=2401,
+        main_heating_category=7,  # electric storage heaters
+        sap_main_heating_code=401,
+    )
+    epc = replace(
+        base,
+        sap_energy_source=replace(base.sap_energy_source, meter_type="1"),  # Dual
+        sap_heating=make_sap_heating(
+            main_heating_details=[storage_main],
+            water_heating_code=950,  # DHW-only heat network (boilers)
+            water_heating_fuel=20,  # EPC "mains gas (community)", as lodged
+        ),
+    )
+
+    # Act
+    standing: float = cert_to_inputs(epc).standing_charges_gbp
+
+    # Assert — £24 off-peak electric (Table 12 note (a)) + £60 half (C6).
+    assert abs(standing - 84.0) <= 1e-9
+
+
 def test_mev_default_data_iuf_is_table_329_system_type_10_value() -> None:
     # Arrange / Act — SAP 10.2 Table 4g note 3 (PDF p.176) directs the
     # default SFP to "the appropriate in-use factor for default data from