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Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minuteA Home Assistant sensor shows unavailable when its integration cannot currently obtain data or its availability logic says the source cannot be reached. The practical fix is to identify the owning integration, read its logs and diagnostics, then verify the device or service, network path and integration-specific availability settings. An unknown state is different: it means Home Assistant does not yet know a value, rather than having confirmed that the source is presently unreachable.
What “unavailable” means in Home Assistant
Entity state is an operational signal, not a measurement. A temperature sensor may still exist in Home Assistant’s entity registry while its state is unavailable because the integration has lost contact, a required dependency failed, or the integration deliberately marked the entity unavailable.
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Home Assistant’s developer guidance draws a useful line: “If we can’t fetch data from a device or service, we should mark it as unavailable.” That rule covers a failed poll, a disconnected gateway, an unreachable cloud API and similar fetch failures. It does not mean the sensor has reported an extreme value, zero, or a bad reading.
Unavailable versus unknown
| State | What it tells you | What to investigate first |
|---|---|---|
| Unavailable | The integration currently cannot obtain data, or its availability logic says the source cannot be reached. | Logs, integration diagnostics, power, network reachability and service status. |
| Unknown | The state is not yet known. A fetch may have succeeded while a particular value is temporarily missing. | Whether the device has produced its first reading, whether a required attribute is absent and what the integration reports after a refresh. |
Check the exact state before changing configuration. Automations, dashboards and templates may react differently to unavailable and unknown, so substituting a numeric fallback can hide the underlying fault.
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A safe first-pass workflow
Use this sequence for any integration. Stop when you find a confirmed cause; changing unrelated settings while the source is offline can create a second problem.
- Record the entity and owner. Note the entity ID, friendly name, integration, device and the time the state changed. In the entity details screen, identify the integration that supplies the entity rather than assuming the dashboard card is the source.
- Confirm the state. Open the entity’s current state and attributes. Verify that the value is unavailable, not unknown, and note whether sibling entities from the same device changed at the same time.
- Read the logs. Open Home Assistant’s log viewer (normally under Settings → System → Logs) and filter attention on the affected integration and the time of failure. Look for authentication errors, timeouts, connection refusals, missing configuration, dependency failures and messages that name a host or topic.
- Download diagnostics when offered. From the integration’s entry under Settings → Devices & services, use its diagnostics action if available. Diagnostics can expose connection state, identifiers, firmware or configuration details that a single error line does not show. Treat diagnostic files as sensitive: they can contain network names, addresses or device identifiers.
- Check the source itself. Confirm that the sensor, hub or service has power and that any status light or local control responds. A battery-powered device may be asleep by design; a mains-powered hub may have rebooted.
- Test reachability from the Home Assistant host. Check the local network, router, Wi-Fi or Ethernet path, DNS and DHCP leases as appropriate. If the integration uses a cloud service, check that provider’s service status and whether the account still authenticates.
- Apply only the integration-specific branch. MQTT availability topics, Z-Wave radio conditions and cloud credentials have different failure modes. Use the branch below that matches the integration named in your logs.
- Retest and document the result. After correcting one cause, wait for the normal polling or message interval, then reload the integration or restart only the relevant device if its documentation calls for that. Record what changed and whether one entity or the whole device recovered.
How to read logs and diagnostics without guessing
A single “connection error” is a direction, not a complete diagnosis. Classify the message before acting:
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| Log evidence | Likely area | Next check |
|---|---|---|
| Authentication, authorization or expired-token message | Account or integration configuration | Reauthenticate through the integration’s documented flow; verify required settings and permissions. |
| Timeout, connection refused or host-not-found message | Device, service or network path | Check power, address, DNS, DHCP lease, firewall and whether the service is reachable from the Home Assistant host. |
| Missing required option, malformed configuration or dependency error | Configuration or software dependency | Correct the named setting, install or repair the required dependency, then reload the integration as documented. |
| Messages that stop after a device reboot | Device or gateway availability | Observe whether the fault returns; recurring failures need the integration’s troubleshooting guidance rather than repeated reboots. |
| Only one entity is unavailable while others from the same source work | Entity-specific capability, attribute or availability rule | Compare the entity’s attributes and diagnostics with a working sibling; do not replace the entire integration immediately. |
Keep the timestamp and the first error in the sequence. Later stack traces are often consequences of the initial disconnect. If diagnostics are unavailable, the ordinary logs and the integration’s own troubleshooting page remain the authoritative starting points.
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Power and physical reachability
Verify the sensor has power, batteries are installed correctly and the hub or bridge is running. For a battery device, wake it or trigger the manufacturer’s normal status action if one exists. For a wired device, check the cable, link indicator and the hub’s local interface. A dashboard refresh cannot repair a source that is switched off.
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Local network checks
Confirm that the Home Assistant host is on the expected network and that the device still has the address or hostname used by the integration. Router changes, a new DHCP lease, DNS failure, VLAN rules and firewall changes can all make a previously working endpoint unreachable. If several integrations became unavailable together, investigate the router, access point, DNS or host connection before editing each entity.
Cloud-backed services
When an integration fetches data from a provider, distinguish a local Home Assistant fault from a provider outage. Check the provider’s status information, account authentication and any recent password, two-factor or permission change. A cloud outage cannot be fixed by changing a local sensor’s unit or dashboard card; wait for service restoration while preserving the relevant log entries.
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MQTT sensors: availability, retained messages and expiry
MQTT has two related but separate flows: a state topic carries the sensor value, while one or more availability topics can tell Home Assistant whether the publishing device is online. A valid state message does not automatically override an availability topic that says the device is offline.
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Check the broker and topic contract
- Confirm that Home Assistant is connected to the intended MQTT broker and that the device is publishing to the topic configured for the sensor.
- Compare the configured online and offline payloads with the exact strings the device publishes. A case difference, extra whitespace or a different spelling can make an online device appear unavailable.
- If multiple availability topics are configured, check
availability_mode.allrequires every configured topic to report online,anyaccepts one online topic, andlatestuses the most recently received availability message. Choose the mode that matches the device’s actual design. - Inspect the broker for the latest state and availability messages. Confirm that the client is publishing after reconnecting, not merely that it published before the outage.
Retained state and the first reading
A retained MQTT state message is delivered immediately when Home Assistant subscribes, so the entity can show the last known value after a restart or resubscription. Without a retained message, the initial state is undefined until the device publishes again. Retention is therefore useful for startup behavior, but it is not proof that the sensor is currently measuring anything; pair it with a correct availability design and an appropriate update interval.
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expire_after and stale publishers
MQTT sensor configuration can use expire_after to mark the entity unavailable after a specified number of seconds without a new state update. The default is no expiry. Set the interval longer than the device’s normal reporting interval and account for expected sleep, broker delay and network jitter. If the value is too short, a healthy low-frequency sensor will repeatedly become unavailable; if it is omitted, a silent publisher can leave an old value present indefinitely.
| Observed MQTT behavior | Interpretation | Action |
|---|---|---|
| Availability says offline | The availability contract is working as configured. | Restore the device or broker path; do not fix this by changing the state value. |
| No retained state after restart | No value is available until the device publishes. | Configure retention if the device and message design support it, or wait for the next scheduled report. |
| Entity expires between normal reports | expire_after is shorter than the real reporting cadence. |
Measure the cadence and increase the expiry window appropriately. |
| State updates arrive but entity remains unavailable | An availability topic or payload is overriding state delivery. | Check topics, online/offline payloads and availability_mode. |
Z-Wave sensors: adapter, firmware and radio checks
Use this branch only when the unavailable entity belongs to a Z-Wave setup. Home Assistant’s compatibility guidance recommends an 800-series Z-Wave adapter with firmware at least 7.23.2. Treat that as a compatibility recommendation, not a universal remedy for MQTT, Wi-Fi, cloud or unrelated integrations.
Verify the adapter and host connection
- Confirm that Home Assistant can see the intended Z-Wave adapter and that the Z-Wave integration is loaded without errors.
- Check the adapter series and firmware against Home Assistant’s supported-adapter information. An older or unsupported combination can create unstable communication even when the sensor itself is powered.
- Review the Z-Wave integration logs for failed commands, node communication errors or controller startup problems before excluding and re-adding a node.
Rule out USB-related radio interference
Home Assistant’s Z-Wave troubleshooting guidance identifies possible radio-frequency interference from a computer’s USB ports. As a focused diagnostic, connect the adapter through a USB extension cable and move it away from the host and other radio-noisy hardware. This test applies to the adapter’s RF environment; it will not correct a bad MQTT topic, an expired cloud credential or a missing sensor configuration.
When an automation fails because a sensor is unavailable
Diagnose the entity before rewriting the automation. Open the automation trace and logs, then inspect the entity’s current state and the device that supplies it. Home Assistant’s automation troubleshooting guidance specifically directs users to check logs, entity state, device power and connection when an entity is unavailable.
- If the trigger depends on a numeric reading, decide how the automation should behave while the state is unavailable. A safety-related action may need an explicit unavailable branch rather than treating it as zero.
- If several entities from one device fail together, repair the device or integration connection first; changing every trigger obscures the common cause.
- If only one entity fails, compare its attributes and availability behavior with a working entity from the same device before changing the automation logic.
A decision table for the most common patterns
| Pattern | Most useful evidence | Focused response |
|---|---|---|
| One sensor unavailable, other integrations normal | That integration’s log and diagnostics; device power. | Repair the named device, credentials or entity-specific configuration. |
| Every entity from one hub unavailable | Hub power, host reachability and integration connection errors. | Restore the hub/network path, then reload the integration if documented. |
| Many unrelated integrations fail together | Router, DNS, DHCP, host networking and cloud status. | Investigate shared infrastructure before individual integrations. |
| MQTT sensor fails after restart | Retained state, broker connection and availability topics. | Correct retention or availability behavior and wait for a new message. |
| Z-Wave nodes become unreliable | Adapter series/firmware, controller logs and physical USB placement. | Meet adapter guidance and test an extension cable for RF interference. |
| Automation stops when the sensor changes state | Entity state, automation trace and logs. | Fix the entity first, then define explicit automation behavior for unavailable or unknown. |
What not to do
- Do not assume unavailable means a bad measurement. It describes data access or availability, not the sensor’s physical reading.
- Do not replace unavailable with a made-up numeric value. A fallback can make charts look healthy while automations act on fiction.
- Do not repeatedly restart Home Assistant without reading the first error. A restart may clear a transient connection while leaving the underlying power, network or configuration fault intact.
- Do not change MQTT expiry or availability mode blindly. Those settings encode the publisher’s timing and online/offline contract.
- Do not buy Z-Wave hardware for a non-Z-Wave problem. Adapter and USB-interference checks are relevant only after the affected integration is identified as Z-Wave.
- Do not exclude and re-include a Z-Wave node as the first step. Preserve logs and diagnostics; re-inclusion can create additional configuration work and does not repair a powered-off controller or blocked network path.
When the evidence is insufficient for a universal fix
There is no single repair that applies to every unavailable sensor. The correct resolution depends on the integration, device model, Home Assistant version and installation method, plus the exact error and timing. If logs show no clear cause, collect the entity ID, integration name, first-failure time, power/network observations and diagnostics (with secrets removed), then follow that integration’s current troubleshooting instructions. This preserves the distinction between a device failure, a service outage, a configuration error and a normal startup state that has not received its first value.
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