Slice S0380.142: §4 (61)m/(59)m cascade — cylinder presence gates combi=0 + primary loss applies for PCDB Table 322 boilers

SAP 10.2 §4 line 7702 (PDF p.137):

  Combi loss for each month from Table 3a, 3b or 3c (enter '0' if
  not a combi boiler)

SAP 10.2 Table 3 (PDF p.160) zero-loss list for primary circuit loss:

  Electric immersion heater
  Combi boiler (including when it is part of a combined heat pump and
  boiler package and provides all the hot water)
  CPSU (including electric CPSU)
  Boiler and thermal store within a single casing
  Separate boiler and thermal store connected by no more than 1.5 m
  of insulated pipework
  Direct-acting electric boiler
  Heat pump (...) with hot water vessel integral to package

Combi boilers are defined by Table 3's zero-loss list entry: they
provide instantaneous DHW with no storage vessel. A cert that lodges
a hot-water cylinder therefore has a non-combi heat generator —
the cylinder bypasses any instantaneous-DHW capability and the
boiler acts as a regular boiler for the DHW circuit.

Two compounding gaps for PCDB Table 322 (gas/oil boiler) records
with a lodged cylinder:

(a) (61)m combi loss: pre-slice the cascade routed every PCDB record
    through `pcdb_combi_loss_override` regardless of cylinder
    presence. For PCDB regular boilers (subsidiary_type=0, store_
    type=0, separate_dhw_tests=0) this dispatched to Table 3a row 1
    "Instantaneous without keep-hot" — 600 kWh/yr. Cert pcdb 1
    (Potterton KOA PCDB 716 + 110 L cylinder) exposed this: worksheet
    (61)m = 0 ; cascade was lodging 600 kWh/yr keep-hot loss on a
    regular oil boiler.

(b) (59)m primary loss: `_primary_loss_applies` gated on
    `main_heating_category in {1, 2}`. The Elmhurst path leaves
    `main_heating_category=None`, so the gate returned False even
    when the cert lodged a PCDB Table 322 (gas/oil boiler) record +
    a cylinder. Worksheet (59)m sum ~1177 kWh ; cascade was zero.

Fix:

- `_water_heating_worksheet_and_gains` now zeroes combi_loss_override
  whenever `epc.has_hot_water_cylinder` is True (top-level gate
  preceding the `pcdb_combi_loss_override` dispatch). Preserves the
  existing non-cylinder fallback for HP / no-PCDB / community-heat
  certs that lack a main_heating_category lodgement.

- `_primary_loss_applies` extends the Elmhurst-path fallback: when
  `main_heating_index_number` resolves to a PCDB Table 322 record,
  return True (the cert is implicitly a boiler — Table 3 row 1 covers
  any "heat generator (e.g. boiler) connected to a hot water storage
  vessel via insulated or uninsulated pipes").

Corpus impact:

- pcdb 1 (Potterton KOA + cylinder, the only PCDB Table 322 + cylinder
  combination in the corpus): SAP +3.40 → +2.86; cost -£75.68 →
  -£63.22; CO2 -397.02 → -328.74; PE -1601.74 → -1257.97.

- Golden cert 0390-2954-3640-2196-4175 (Firebird oil combi PCDF 9005
  + cylinder): PE -26.37 → -28.50; CO2 -2.55 → -2.75. Combi-loss
  removal (-600 kWh/yr) exceeded the primary-loss gain (~5-10 kWh
  given the cert's insulated pipework + thermostat lodging), so the
  net (62) shifted down. Direction is more spec-correct: the spec
  treats a combi feeding a cylinder as a regular boiler for DHW,
  matching the (61)m=0 + (59)m>0 worksheet behaviour.

Extended handover suite: 885 pass, 0 fail.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/documents_parser/tests/test_heating_systems_corpus.py

@@ -233,7 +233,7 @@ _EXPECTATIONS: tuple[_CorpusExpectation, ...] = (
     _CorpusExpectation(variant='oil pcdb 1', block='11a', expected_sap_resid=+0.4239, expected_cost_resid_gbp=-9.7668, expected_co2_resid_kg=-35.9551, expected_pe_resid_kwh=-83.8239),
     _CorpusExpectation(variant='oil pcdb 2', block='11a', expected_sap_resid=+0.4239, expected_cost_resid_gbp=-9.7668, expected_co2_resid_kg=-35.9551, expected_pe_resid_kwh=-83.8239),
     _CorpusExpectation(variant='oil pcdb 3', block='11a', expected_sap_resid=+1.1597, expected_cost_resid_gbp=-26.7204, expected_co2_resid_kg=-53.1709, expected_pe_resid_kwh=-271.4351),
-    _CorpusExpectation(variant='pcdb 1', block='11a', expected_sap_resid=+3.3965, expected_cost_resid_gbp=-75.6799, expected_co2_resid_kg=-397.0228, expected_pe_resid_kwh=-1601.7416),
+    _CorpusExpectation(variant='pcdb 1', block='11a', expected_sap_resid=+2.8556, expected_cost_resid_gbp=-63.2154, expected_co2_resid_kg=-328.7435, expected_pe_resid_kwh=-1257.9712),
     # Slice S0380.133 unblocked 10 solid-fuel variants by routing the
     # Elmhurst §14.0 "Main Heating EES Code" through the new
     # `_ELMHURST_MAIN_HEATING_EES_TO_FUEL_CODE` dict. Pre-slice the

domain/sap10_calculator/rdsap/cert_to_inputs.py

@@ -3649,7 +3649,7 @@ def _primary_loss_applies(
     cylinder_present: bool,
     hp_record: Optional[HeatPumpRecord],
 ) -> bool:
-    """SAP 10.2 Table 3 (PDF p.159) zero-loss configurations — primary
+    """SAP 10.2 Table 3 (PDF p.160) zero-loss configurations — primary
     loss only fires when a cylinder is present AND the lodgement falls
     outside the zero list. The cohort path: heat-pump main heating with
     a separate (not integral) vessel per the PCDB Table 362 record.
@@ -3657,11 +3657,19 @@ def _primary_loss_applies(
     Combi boilers, CPSUs, thermal stores within 1.5 m insulated pipe,
     direct-acting electric boilers, electric immersion heaters, and
     HPs with `hw_vessel_mode = 1` (integral) all skip the loss. For
-    cohort coverage we model two paths:
+    cohort coverage we model three paths:
         - HP with PCDB record: gate on `hp_record.hw_vessel_mode != 1`
         - Boiler (cat 1, 2) with cylinder: primary loss applies (the
           cascade's pre-slice-102d behaviour was zero, masking ~516
           kWh/yr on certs with cylinders).
+        - PCDB Table 322 (gas/oil boiler) record with cylinder, when
+          main_heating_category is not lodged: primary loss applies
+          (cylinder presence + PCDB boiler = "boiler connected to hot-
+          water storage vessel" per Table 3 row 1 — the spec category
+          for this fixture is 1, but the Elmhurst mapper currently
+          leaves `main_heating_category=None`, so the cascade dispatch
+          falls through to this branch instead of the boiler-category
+          branch above).
     """
     if not cylinder_present:
         return False
@@ -3676,7 +3684,18 @@ def _primary_loss_applies(
         # Spec p.159: zero for "Heat pump from PCDB with hot water vessel
         # integral to package". Vessel mode 1 = integral.
         return hp_record.hw_vessel_mode != 1
-    return main.main_heating_category in {1, 2}
+    if main.main_heating_category in {1, 2}:
+        return True
+    # Elmhurst-path fallback: when the cert lodges a PCDB Table 322
+    # record (gas/oil boiler) but `main_heating_category` is None, the
+    # presence of the PCDB boiler record is sufficient evidence that
+    # the main is a boiler — Table 3 row 1 applies ("hot water is
+    # heated by a heat generator (e.g. boiler) connected to a hot
+    # water storage vessel via insulated or uninsulated pipes").
+    if main.main_heating_index_number is not None:
+        if gas_oil_boiler_record(main.main_heating_index_number) is not None:
+            return True
+    return False
 
 
 # RdSAP 10 §10.11 Table 29 "Heating and hot water parameters" row
@@ -3901,13 +3920,27 @@ def _water_heating_worksheet_and_gains(
         daily_hot_water_monthly_l_per_day=bootstrap.daily_hot_water_l_per_day_monthly,
     )
     main = _first_main_heating(epc)
-    # SAP 10.2 §4 line 7702: non-combi main heating → (61)m = 0. Without
-    # this gate the cascade falls through to `combi_loss_monthly_kwh_table_
-    # 3a_keep_hot_time_clock()` (600 kWh/yr) on every cert lacking a PCDB
-    # Table 105 boiler record — including all heat pump certs.
-    if combi_loss_override is None and not _table_3a_combi_loss_default_applies(
+    # SAP 10.2 §4 line 7702 (PDF p.137): "Combi loss for each month
+    # from Table 3a, 3b or 3c (enter '0' if not a combi boiler)". The
+    # SAP 10.2 Table 3 zero-loss list (PDF p.160) defines a combi boiler
+    # by its instantaneous-DHW operation: combis don't feed a cylinder
+    # because their heat exchanger heats DHW on demand. A lodged hot-
+    # water cylinder therefore means the heat generator is NOT a combi
+    # — even when the cert lodges a PCDB Table 105 record that would
+    # otherwise route through `pcdb_combi_loss_override` to a Table 3a/
+    # 3b/3c row. Cert pcdb 1 (Potterton KOA PCDB 716 + 110 L cylinder)
+    # exposes this: pre-slice the cascade applied Table 3a row 1
+    # 600 kWh/yr "keep-hot" loss to a PCDB regular oil boiler.
+    if epc.has_hot_water_cylinder:
+        combi_loss_override = zero_monthly
+    elif combi_loss_override is None and not _table_3a_combi_loss_default_applies(
         main
     ):
+        # SAP 10.2 §4 line 7702 fallback: non-combi main heating → (61)m
+        # = 0. Without this gate the cascade falls through to `combi_
+        # loss_monthly_kwh_table_3a_keep_hot_time_clock()` (600 kWh/yr)
+        # on every cert lacking a PCDB Table 105 boiler record —
+        # including all heat pump certs.
         combi_loss_override = zero_monthly
     # SAP 10.2 §4 lines 7670-7693 + Tables 2/2a/2b — cylinder storage loss
     # (56)m. Spec p.135 instructs entering 0 in (47) for instantaneous /

domain/sap10_calculator/rdsap/tests/test_cert_to_inputs.py

@@ -2844,6 +2844,129 @@ def test_sap_9_4_11_no_boiler_interlock_applies_minus_5_pcdb_space_heating_when_
     # PCDB Eq D1 step.
 
 
+def test_sap_4_lines_7700_7702_pcdb_regular_boiler_with_cylinder_zeroes_combi_loss_and_applies_primary_loss() -> None:
+    """SAP 10.2 §4 line 7702 (PDF p.137):
+
+        Combi loss for each month from Table 3a, 3b or 3c
+        (enter "0" if not a combi boiler)
+
+    SAP 10.2 Table 3 (PDF p.160) "Primary circuit loss":
+
+        Primary circuit loss applies when hot water is heated by a
+        heat generator (e.g. boiler) connected to a hot water storage
+        vessel via insulated or uninsulated pipes (the primary
+        pipework). Primary loss is set to zero for the following:
+            Electric immersion heater
+            Combi boiler ...
+            CPSU ...
+            Boiler and thermal store within a single casing
+            Separate boiler and thermal store connected by no more
+            than 1.5 m of insulated pipework
+            Direct-acting electric boiler
+            Heat pump (...) with hot water vessel integral to package
+
+    A PCDB regular gas/oil boiler (Table 322) feeding a hot-water
+    cylinder is in neither of the (61)m / (59)m zero-loss lists:
+        - cylinder presence → not a combi → (61)m = 0
+        - boiler + cylinder + indirect pipework → (59)m applies
+
+    Pre-slice the cascade routed PCDB 716 (Potterton KOA, a regular
+    oil boiler) through `pcdb_combi_loss_override` and got 600 kWh/yr
+    "Table 3a row 1 keep-hot" (the spec's *combi* fall-through),
+    while `_primary_loss_applies` returned False because the Elmhurst
+    mapper leaves `main_heating_category=None` (cascade gates primary
+    on `main_heating_category in {1, 2}`). Both gaps masked one
+    another: −1177 kWh missing primary + +600 kWh excess combi netted
+    to ~−577 kWh on (62).
+
+    This slice introduces the cylinder-presence gate for combi loss
+    (combi boilers are by definition instantaneous per Table 3
+    zero-loss list — a lodged cylinder means the heat generator is
+    not a combi) and extends primary-loss eligibility to detect PCDB
+    Table 322 (gas/oil boiler) records when the cascade can't read
+    main_heating_category from the cert (Elmhurst path).
+    """
+    # Arrange — pcdb 1 corpus variant: PCDB 716 Potterton KOA + 110 L
+    # cylinder + Cylinder Stat: No (worksheet shows (61)m all zero
+    # and (59)m monthly = 128.38 / 115.95 / 128.38 / ...; annual sum
+    # ≈ 1176.79 kWh/yr).
+    import re
+    import subprocess
+    from pathlib import Path
+
+    from backend.documents_parser.elmhurst_extractor import ElmhurstSiteNotesExtractor
+    from datatypes.epc.domain.mapper import EpcPropertyDataMapper
+    from domain.sap10_calculator.tables.pcdb import gas_oil_boiler_record
+
+    corpus_pcdb_1 = (
+        Path(__file__).parents[4]
+        / "sap worksheets/heating systems examples/pcdb 1"
+    )
+    summary_pdf = next(corpus_pcdb_1.glob("Summary_*.pdf"))
+    info = subprocess.run(
+        ["pdfinfo", str(summary_pdf)], capture_output=True, text=True, check=True,
+    ).stdout
+    pc = int(re.search(r"Pages:\s+(\d+)", info).group(1))  # type: ignore[union-attr]
+    pages: list[str] = []
+    for i in range(1, pc + 1):
+        layout = subprocess.run(
+            ["pdftotext", "-layout", "-f", str(i), "-l", str(i),
+             str(summary_pdf), "-"],
+            capture_output=True, text=True, check=True,
+        ).stdout
+        tokens: list[str] = []
+        for line in layout.splitlines():
+            if not line.strip():
+                tokens.append("")
+                continue
+            parts = [p for p in re.split(r"\s{2,}", line.strip()) if p]
+            tokens.extend(parts)
+        pages.append("\n".join(tokens))
+    notes = ElmhurstSiteNotesExtractor(pages).extract()
+    epc = EpcPropertyDataMapper.from_elmhurst_site_notes(notes)
+
+    # Act — drive (45..65) directly via the §4 worksheet helper so the
+    # combi-loss and primary-loss assertions read the per-month tuples
+    # the cascade hands to `total_water_heating_demand_monthly_kwh`.
+    main = epc.sap_heating.main_heating_details[0]
+    pcdb_record = (
+        gas_oil_boiler_record(main.main_heating_index_number)
+        if main.main_heating_index_number is not None
+        else None
+    )
+    wh_result, _ = _water_heating_worksheet_and_gains(
+        epc=epc,
+        water_efficiency_pct=0.53,
+        is_instantaneous=False,
+        primary_age="G",
+        pcdb_record=pcdb_record,
+    )
+    assert wh_result is not None
+
+    # Assert 1 — (61)m all zero per §4 line 7702 ("enter '0' if not a
+    # combi boiler"). A lodged cylinder means the heat generator is
+    # not a combi (combi boilers are instantaneous per Table 3
+    # zero-loss list).
+    assert sum(wh_result.combi_loss_monthly_kwh) == 0.0, (
+        f"pcdb 1 combi loss annual: got {sum(wh_result.combi_loss_monthly_kwh)!r}, "
+        f"want 0.0 per SAP 10.2 §4 line 7702 (cylinder lodged → main is "
+        f"not a combi boiler → (61)m = 0)"
+    )
+
+    # Assert 2 — (59)m annual ≈ 1176.79 kWh per Table 3 + RdSAP §S10.11
+    # Table 29 defaults (uninsulated pipework p=0 for age G; no cylinder
+    # thermostat → winter h=11, summer h=3). Worksheet pcdb 1 sum =
+    # Jan 128.38 + Feb 115.95 + ... + Dec 128.38 ≈ 1176.79.
+    expected_primary_annual = 1176.79
+    got_primary_annual = sum(wh_result.primary_loss_monthly_kwh)
+    assert abs(got_primary_annual - expected_primary_annual) < 1.0, (
+        f"pcdb 1 primary loss annual: got {got_primary_annual!r}, "
+        f"want {expected_primary_annual!r} per SAP 10.2 Table 3 "
+        f"(PCDB gas/oil boiler + cylinder + uninsulated primary pipework + "
+        f"no cylinder thermostat)"
+    )
+
+
 def test_cylinder_storage_loss_applies_57m_solar_adjustment_per_sap_4_line_7693() -> None:
     """SAP 10.2 §4 line 7693 (PDF p.137):
 

domain/sap10_calculator/rdsap/tests/test_golden_fixtures.py

@@ -127,8 +127,8 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
         cert_number="0390-2954-3640-2196-4175",
         actual_sap=60,
         expected_sap_resid=+7,
-        expected_pe_resid_kwh_per_m2=-26.3749,
-        expected_co2_resid_tonnes_per_yr=-2.5544,
+        expected_pe_resid_kwh_per_m2=-28.5027,
+        expected_co2_resid_tonnes_per_yr=-2.7481,
         notes=(
             "Detached, TFA 360, age F, Firebird oil combi PCDF 9005 "
             "(winter eff 86.4%). PCDB record lodges separate_dhw_tests=0 + "
@@ -141,11 +141,16 @@ _EXPECTATIONS: tuple[_GoldenExpectation, ...] = (
             "53 → 54 (resid -7 → -6). Slice S0380.131 flipped heating-oil "
             "tariff 7.64 → 5.44 (cert 0240 closed exactly), exposing this "
             "cert's previously-masked +13 SAP of cascade gaps: residual "
-            "swung -6 → +7. The oil-price bug was netting against an "
-            "opposite-direction gap (cert lodges age F + 360 m² detached "
-            "+ Firebird PCDF — likely fabric or hot-water cascade). PE / "
-            "CO2 residuals unchanged by the unit-price flip; remaining "
-            "SAP residual is a follow-up slice candidate."
+            "swung -6 → +7. Slice S0380.142 re-routed this cert via the "
+            "SAP 10.2 §4 line 7702 cylinder-presence gate ((61)m = 0 since "
+            "the combi feeds a cylinder → not a combi for DHW per Table 3) "
+            "+ Table 3 row 1 primary loss (PCDB Table 322 boiler + cylinder "
+            "→ primary loss applies). The combi-loss removal (-600 kWh/yr) "
+            "exceeded the primary-loss gain → cascade HW fuel dropped "
+            "~650 kWh; PE residual shifted -26.37 → -28.50, CO2 -2.55 → "
+            "-2.75. SAP integer unchanged because the cascade was already "
+            "well above SAP 60 (actual). Remaining residual is a fabric or "
+            "different §4 driver — follow-up slice candidate."
         ),
     ),
     _GoldenExpectation(