diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index 5bb76429d..22d379c32 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -7126,6 +7126,20 @@ def _cylinder_storage_loss_override(
         insulation_label, thickness_mm = "loose_jacket", 0.0
     if insulation_label is None and thickness_mm == 0.0:
         insulation_label = "loose_jacket"
+    # RdSAP 10 Table 29 (PDF p.56) "Hot water cylinder insulation if not
+    # accessible": a lodged cylinder with NO insulation data at all takes
+    # the age-band default — the same row the §10.7 no-water-heating
+    # default uses. An ABSENT thickness means not accessible (Table 29);
+    # a lodged 0 mm means uninsulated (handled above). When the age band
+    # itself is unresolvable, fall through to the legacy None (zero loss)
+    # rather than raising mid-rebaseline.
+    if insulation_label is None and thickness_mm is None:
+        band = (_dwelling_age_band(epc) or "")[:1].upper()
+        table_29_default = _TABLE_29_DEFAULT_CYLINDER_INSULATION_BY_AGE.get(band)
+        if table_29_default is not None:
+            default_code, default_mm = table_29_default
+            insulation_label = _cylinder_storage_loss_insulation_label(default_code)
+            thickness_mm = float(default_mm)
     if insulation_label is None:
         return None
     if thickness_mm is None: