diff --git a/c6_cohort.py b/c6_cohort.py
deleted file mode 100644
index 25c18c5cd..000000000
--- a/c6_cohort.py
+++ /dev/null
@@ -1,41 +0,0 @@
-"""Which 21.0.1-corpus certs are in #1606's C6 half-charge cohort?
-Cohort = WHC in {950,951,952} AND space main is NOT a heat network.
-"""
-import json
-from pathlib import Path
-from datatypes.epc.domain.mapper import EpcPropertyDataMapper
-from datatypes.epc.domain.field_mappings import is_heat_network_main
-from domain.sap10_calculator.rdsap.cert_to_inputs import (
-    _first_main_heating, _heat_network_standing_charge_gbp,
-    _WATER_HEAT_NETWORK_ONLY_CODES,
-)
-
-path = Path("backend/epc_api/json_samples/RdSAP-Schema-21.0.1/corpus.jsonl")
-certs = [json.loads(l) for l in path.read_text().splitlines() if l.strip()]
-
-hits = []
-for c in certs:
-    epc = EpcPropertyDataMapper.from_api_response(c)
-    whc = epc.sap_heating.water_heating_code if epc.sap_heating else None
-    if whc not in _WATER_HEAT_NETWORK_ONLY_CODES:
-        continue
-    m1 = _first_main_heating(epc)
-    net = is_heat_network_main(m1)
-    hits.append({
-        "rrn": c.get("rrn") or c.get("lmk_key"),
-        "uprn": c.get("uprn"),
-        "addr": (c.get("address1") or "")[:34],
-        "whc": whc,
-        "main_code": m1.sap_main_heating_code if m1 else None,
-        "main_is_network": net,
-        "net_standing": _heat_network_standing_charge_gbp(epc, m1),
-        "in_C6_half_cohort": not net,
-    })
-
-print(f"WHC 950/951/952 certs in 21.0.1 corpus: {len(hits)}\n")
-for h in hits:
-    flag = "  <== C6 HALF COHORT" if h["in_C6_half_cohort"] else ""
-    print(f"  rrn={h['rrn']} uprn={h['uprn']}")
-    print(f"    addr={h['addr']!r} whc={h['whc']} main={h['main_code']} "
-          f"network_main={h['main_is_network']} net_standing={h['net_standing']}{flag}")
-print(f"\nIn C6 half cohort: {sum(h['in_C6_half_cohort'] for h in hits)}")
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 9bfa07707..0ae21a4fe 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -7723,15 +7723,12 @@ def _fuel_cost(
         table_32_unit_price_p_per_kwh(60) * _PENCE_TO_GBP
     )
 
-    heat_network_standing = _heat_network_standing_charge_gbp(epc, main)
-    standing = (
-        heat_network_standing
-        if heat_network_standing is not None
-        else additional_standing_charges_gbp(
-            main_fuel_code=main_fuel_code,
-            water_heating_fuel_code=water_heating_fuel_code,
-            tariff=tariff,
-        )
+    standing = _standing_charges_total_gbp(
+        epc,
+        main,
+        main_fuel_code=main_fuel_code,
+        water_heating_fuel_code=water_heating_fuel_code,
+        tariff=tariff,
     )
 
     # Worksheet display convention: when a row's kWh is zero (no main 2, no