Template Sensors - Attributes When Passed As Variables Evaluate To "unavailable"

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The Problem

When passing sensor states and attributes as variables into a template sensor in Home Assistant, a peculiar behavior is observed. The sensor attributes evaluate to "unavailable" in certain scenarios, while in others, they return the correct value of the sensor or attribute. This article delves into the issue, providing a detailed analysis of the problem, its occurrence in specific versions of Home Assistant Core, and the necessary steps to resolve it.

The Issue in Home Assistant Core

The issue is observed in Home Assistant Core version core-2025.5.0. The problem arises when using template sensors with variables that reference sensor attributes. In this version, the attributes evaluate to "unavailable" when passed as variables, whereas they return the correct value when directly referenced in the template sensor.

Example YAML Snippets

To better understand the issue, let's examine the following YAML snippets:

- unique_id: plop_attribute_test_1
  variables:
    descriptor: "{{ state_attr('sensor.weather_data', 'condition_0') }}"
  state: >
    {{ descriptor }}

- unique_id: plop_attribute_test_2
  state: >
    {{ state_attr('sensor.weather_data', 'condition_0') }}

- unique_id: plop_state_test_1
  variables:
    descriptor: "{{ states('sensor.rutherglen_icon_descriptor_0') }}"
  state: > 
    {{ descriptor }}

- unique_id: plop_state_test_2
  variables:
    descriptor: 
  state: >
    {{ states('sensor.rutherglen_icon_descriptor_0') }}

In the first snippet, the attribute condition_0 is passed as a variable, resulting in "unavailable." In contrast, the second snippet directly references the attribute, returning the correct value. Similarly, the third and fourth snippets demonstrate the same behavior, with the variable passing resulting in "unavailable" and direct referencing returning the correct value.

Resolving the Issue

To resolve this issue, you can follow these steps:

  1. Update Home Assistant Core: Ensure you are running the latest version of Home Assistant Core. If you are using version core-2025.5.0, update to the latest version.
  2. Directly Reference Attributes: Instead of passing attributes as variables, directly reference them in the template sensor. This approach ensures that the attributes return the correct value.
  3. Use the states Function: When referencing states, use the states function instead of state_attr. This function provides a more reliable way to access state attributes.

Example Solution

Here's an updated YAML snippet that resolves the issue:

- unique_id: plop_attribute_test_1
  state: >
    {{ state_attr('sensor.weather_data', 'condition_0') }}

- unique_id: plop_state_test_1
  state: > 
    {{ states('sensor.rutherglen_icon_descriptor_0') }}

By following these steps and using the provided examples, you should be able to resolve the issue of template sensors attributes to "unavailable" when passed as variables.

Conclusion

Frequently Asked Questions

Q: What is the issue with template sensors in Home Assistant Core?

A: The issue arises when passing sensor states and attributes as variables into a template sensor. In certain scenarios, the attributes evaluate to "unavailable," while in others, they return the correct value of the sensor or attribute.

Q: Which version of Home Assistant Core is affected by this issue?

A: The issue is observed in Home Assistant Core version core-2025.5.0.

Q: What is the difference between passing attributes as variables and directly referencing them in a template sensor?

A: When passing attributes as variables, they evaluate to "unavailable" in certain scenarios. In contrast, directly referencing attributes in a template sensor returns the correct value.

Q: How can I resolve this issue?

A: To resolve this issue, you can follow these steps:

  1. Update Home Assistant Core: Ensure you are running the latest version of Home Assistant Core. If you are using version core-2025.5.0, update to the latest version.
  2. Directly Reference Attributes: Instead of passing attributes as variables, directly reference them in the template sensor. This approach ensures that the attributes return the correct value.
  3. Use the states Function: When referencing states, use the states function instead of state_attr. This function provides a more reliable way to access state attributes.

Q: What is the states function, and how does it differ from state_attr?

A: The states function is used to access state attributes in a more reliable way. It provides a more flexible and efficient way to access state attributes compared to state_attr.

Q: Can I use the states function with sensor attributes?

A: Yes, you can use the states function with sensor attributes. This function provides a more reliable way to access state attributes, including sensor attributes.

Q: Are there any other solutions to this issue?

A: Yes, there are other solutions to this issue. You can also use the template sensor with the source parameter set to sensor to access sensor attributes.

Q: How can I troubleshoot this issue?

A: To troubleshoot this issue, you can check the Home Assistant logs for any errors or warnings related to the template sensor. You can also use the debug mode to enable debugging for the template sensor.

Q: Can I get more information about this issue?

A: Yes, you can get more information about this issue by checking the Home Assistant documentation and community forums. You can also reach out to the Home Assistant support team for further assistance.

Conclusion

The issue of template sensors evaluating attributes to "unavailable" when passed as variables is a known problem in Home Assistant Core version core-2025.5.0. By directly referencing attributes, using the states function, and updating to the latest version of Home Assistant Core, you can resolve this issue and ensure that your template sensors return the correct values. If you have any further questions or concerns, feel free to ask.