diff --git a/opencode/decisions.yaml b/opencode/decisions.yaml
index 44507004..5b7214e4 100644
--- a/opencode/decisions.yaml
+++ b/opencode/decisions.yaml
@@ -579,3 +579,25 @@ notes:
       - webrtc
     pin: true
     status: active
+  - id: 2026-08-28-filter-plug-is-hardware-faulty-replace
+    date: 2026-08-28
+    title: Filter plug is hardware-faulty; replace as "Air Purifier"
+    decision: 'The Filter plug (0xffffb40e060893d8, switch.filter) is hardware-faulty:
+      downlink fails with MAC_CHANNEL_ACCESS_FAILURE (0xe1) despite clean re-pair and
+      relocation; uplink/button/other devices work. Do not re-diagnose. Scheduled for
+      replacement, to be named "Air Purifier".'
+    rationale: Clean re-pair and relocation next to the coordinator both failed to resolve
+      identical 0xe1 errors on downlink-only commands; physical button and uplink
+      telemetry work, and no other device shares the fault. Diagnosis of a defective
+      receive/ack path is final. Replacement gets a new IEEE, so
+      zigbee2mqtt/configuration.yaml must be re-pointed to it and the name set to "Air
+      Purifier".
+    entities:
+      - switch.filter
+      - sensor.0xffffb40e060893d8_linkquality
+    files:
+      - zigbee2mqtt/configuration.yaml
+    integrations:
+      - zigbee2mqtt
+    pin: true
+    status: active