diff --git a/harness/report.py b/harness/report.py
index c93f0d02..002cbd22 100644
--- a/harness/report.py
+++ b/harness/report.py
@@ -153,6 +153,17 @@ def _triggers_for(epc: EpcPropertyData, measure_type: str) -> dict[str, Any]:
                 epc.sap_heating.main_heating_details[0].main_heating_category
             ),
         }
+    if measure_type == "gas_boiler_upgrade":
+        # heating_recommendation.py offers a gas condensing boiler to a dwelling
+        # with an existing (non-electric) wet boiler and a mains-gas connection;
+        # the cylinder presence shapes it (combi vs regular + cylinder fixes).
+        return {
+            "sap_main_heating_code": (
+                epc.sap_heating.main_heating_details[0].sap_main_heating_code
+            ),
+            "mains_gas": epc.sap_energy_source.mains_gas,
+            "has_hot_water_cylinder": epc.has_hot_water_cylinder,
+        }
     return {}
 
 
diff --git a/tests/harness/test_report.py b/tests/harness/test_report.py
index 4357b4f7..1dcf9123 100644
--- a/tests/harness/test_report.py
+++ b/tests/harness/test_report.py
@@ -15,6 +15,9 @@ from harness.report import (
     format_report_markdown,
     parity_report_for,
 )
+from tests.domain.modelling._elmhurst_recommendation import (
+    parse_recommendation_summary,
+)
 
 _GOLDEN = (
     Path(__file__).resolve().parents[1]
@@ -99,6 +102,29 @@ def test_each_fired_measure_carries_the_attributes_that_triggered_it() -> None:
     }
 
 
+def test_gas_boiler_upgrade_surfaces_its_eligibility_triggers() -> None:
+    # No golden API cert selects the boiler upgrade (it competes with — and on
+    # houses loses to — the ASHP bundle within the one heating Recommendation),
+    # so the trigger branch is exercised directly, like the cert_to_inputs unit
+    # tests of internal helpers.
+    from harness.report import _triggers_for  # pyright: ignore[reportPrivateUsage]
+
+    # Arrange — a mains-gas wet boiler (SAP code 114) with a hot-water cylinder:
+    # the boiler-upgrade eligibility attributes the report should explain.
+    epc = parse_recommendation_summary("boiler_cyl_gas_001431_before.pdf")
+
+    # Act
+    triggers = _triggers_for(epc, "gas_boiler_upgrade")
+
+    # Assert — the wet-boiler SAP code, the mains-gas connection that makes the
+    # gas end-state installable, and the cylinder that shapes the bundle.
+    assert triggers == {
+        "sap_main_heating_code": 114,
+        "mains_gas": True,
+        "has_hot_water_cylinder": True,
+    }
+
+
 def test_few_measure_cert_surfaces_only_its_fired_measures_triggers() -> None:
     # Arrange
     path: Path = _GOLDEN / f"{_WITHIN_TOLERANCE}.json"