Automation was not triggered (template)

Configuration Blueprints
1

I was trying to create a blueprint automation to control the exhaust fan in the bathroom that turns off if the dew point drops below a threshold, but the fan would have to be on for a specific time before that (15 minutes). I have set up the automation as below, but the automation only triggered once, when it past the 15-minute on condition. It was never triggered again when the dew point drops below the level.

trigger:
  - platform: state
    entity_id: fan.master_bedroom_vent_fan
    to: 'on'
    for:
      hours: 0
      minutes: 15
      seconds: 0
  - platform: template
    value_template: >-
      {{ (states(actual_dp)|float - states(bl_dp)|float)|round(1) <= threshold
      }}
condition:
  - condition: and
    conditions:
      - condition: state
        entity_id: fan.master_bedroom_vent_fan
        state: 'on'
        for:
          hours: 0
          minutes: 15
          seconds: 0
      - condition: template
        value_template: >-
          {{ (states(actual_dp)|float - states(bl_dp)|float)|round(1) <=
          threshold }}
action:
  - service: homeassistant.turn_off
    entity_id: fan.master_bedroom_vent_fan
variables:
  bl_dp: sensor.master_bedroom_dew_point
  actual_dp: sensor.master_bedroom_ensuite_dew_point
  target_fan: fan.master_bedroom_vent_fan
  threshold: 2
mode: restart

May I know what is missing? I thought the HA would evaluate the template every time any entity inside the template changes.

2

For values that need to be available to template triggers you should use Trigger Variables.

trigger_variables:
  bl_dp: sensor.master_bedroom_dew_point
  actual_dp: sensor.master_bedroom_ensuite_dew_point
  target_fan: fan.master_bedroom_vent_fan
  threshold: 2
trigger:
  - platform: state
    entity_id: fan.master_bedroom_vent_fan
    to: 'on'
    for:
      hours: 0
      minutes: 15
      seconds: 0
  - platform: template
    value_template: >-
      {{ (states(actual_dp)|float - states(bl_dp)|float)|round(1) <= threshold }}
condition:
  - condition: state
    entity_id: fan.master_bedroom_vent_fan
    state: 'on'
    for:
      hours: 0
      minutes: 15
      seconds: 0
  - condition: template
    value_template: >-
      {{ (states(actual_dp)|float - states(bl_dp)|float)|round(1) <= threshold }}
action:
  - service: homeassistant.turn_off
    entity_id: fan.master_bedroom_vent_fan
mode: restart
3

I would add that float should have a default value to keep from errors and log spam
(states(actual_dp)|float(1) ...

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