TemplateError: UndefinedError: 'HW' is undefined

Configuration
1

I have upgraded to HA2026.4.4 from the last HA2026.3 version.
Now found below error in the logs which occurs 300 times a day!
Last line says HW is undefined but it doesn't mention any integration or something, where to look??

2026-05-08 09:57:42.347 ERROR (MainThread) [homeassistant.helpers.event] Error while processing template: Template<template=({{ HW }}) renders=4218>
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/template/__init__.py", line 465, in async_render
    render_result = render_with_context(self.template, compiled, **kwargs)
  File "/usr/src/homeassistant/homeassistant/helpers/template/context.py", line 45, in render_with_context
    return template.render(**kwargs)
           ~~~~~~~~~~~~~~~^^^^^^^^^^
  File "/usr/local/lib/python3.14/site-packages/jinja2/environment.py", line 1295, in render
    self.environment.handle_exception()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/usr/local/lib/python3.14/site-packages/jinja2/environment.py", line 942, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "<template>", line 1, in top-level template code
jinja2.exceptions.UndefinedError: 'HW' is undefined
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
  File "/usr/src/homeassistant/homeassistant/helpers/template/__init__.py", line 583, in async_render_to_info
    render_info._result = self.async_render(  # noqa: SLF001
                          ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
        variables, strict=strict, log_fn=log_fn, **kwargs
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/src/homeassistant/homeassistant/helpers/template/__init__.py", line 467, in async_render
    raise TemplateError(err) from err
homeassistant.exceptions.TemplateError: UndefinedError: 'HW' is undefined
2

It's not a template snippet sitting in your Developer Tools / Template Editor is it?

3

No unfortunately not, that would be easy.
Although I will wipe everything there and see what happens.

I do have a min/max sensor which has one entity unavailable at the moment due disconnected solar panels. That should not generate this error I assume.

4

This is likely a template in your UI somewhere, MQTT discovery, or an automation/script variable. That template will not naturally update like it says it is.

That template in the backend would only render once unless attached to a trigger. I.e. It would only render once from the template editor, it would only render once from a template entity without a trigger.

So that means you should be looking in the UI for custom cards that have refresh rates associated with them (Not markdown card), MQTT entities that watch topics, or automations variable that trigger frequently.

5

thanks.
That limits it and I then assume it has something to do with an automation catching the DSMR-power sensor (1/sec) and setting another sensor for battery load/discharge power.
At first I will disable those two automations and see what happens.

6

Why not just look in the automation for the template? Or you could post it here, it shouldn't take long for us to find the problem.