If you are posting code, use the code tags and not quotes. That way you can pick out errors with indentations more easily. Like the first part:
setpoint_cv_virtual:
friendly_name: "CV Virtual Setpoint"
unit_of_measurement: "°C"
value_template: >
{% set woonkamer_td = (state_attr('climate.woonkamer_bt','temperature') - states('sensor.living_room_temperature') | float) %}
{% set berging_td = (state_attr('climate.berging_bt','temperature') - states('sensor.berging_mija_temp_temperature') | float) %}
{% set slaapkamer_td = (state_attr('climate.slaapkamer','temperature') - states('sensor.mbr_temperature') | float) %}
{% set badkamer_td = (state_attr('climate.badkamer_bt','temperature') - states('sensor.badkamer_mija_temp_temperature') | float) %}
{% set inkomhall_td = (state_attr('climate.inkomhall','temperature') - states('sensor.inkomhal_radiator_local_temperature') | float) %}
{% set fitness_td = (state_attr('climate.fitness','temperature') - states('sensor.fitness_temperature') | float) %}
{% set max_td = ([woonkamer_td,berging_td,slaapkamer_td,badkamer_td,inkomhall_td,fitness_td] | max) %}
{% set list_room_td = [woonkamer_td,berging_td,slaapkamer_td,badkamer_td,inkomhall_td,fitness_td] %}
{% set index_td = list_room_td.index(max_td) %}
{% if index_td == 1 %}
{{ state_attr('climate.woonkamer_bt','temperature') }}
{% elif index_td == 2 %}
{{ state_attr('climate.berging_bt','temperature') }}
{% elif index_td == 3 %}
{{ state_attr('climate.slaapkamer','temperature') }}
{% elif index_td == 4 %}
{{ state_attr('climate.badkamer_bt','temperature') }}
{% elif index_td == 5 %}
{{ state_attr('climate.inkomhall','temperature') }}
{% else %}
{{ state_attr('climate.fitness','temperature') }}
{% endif %}
Having said that, you never seemed to define this is a template sensor.
Keep in mind that my code is old and had a few revisions. Important thing is to add default values so these get used when sensors are offline.
- platform: template
sensors:
setpoint_cv_virtual:
friendly_name: "CV Virtual Setpoint"
unit_of_measurement: "°C"
value_template: >
{% set alex_td = state_attr('climate.alex','temperature') | float(18) - states('sensor.alex_sensor_temperature') | float(18) %}
{% set esther_td = state_attr('climate.esther','temperature') | float(18) - states('sensor.esther_sensor_temperature') | float(18) %}
{% set woonkamer_td = state_attr('climate.woonkamer','temperature') | float(18) - states('sensor.woonkamer_sensor_temperature') | float(18) %}
{% set max_td = ([woonkamer_td,alex_td,esther_td] | max) %}
{% set list_room_td = [woonkamer_td,alex_td,esther_td] %}
{% set index_td = list_room_td.index(max_td) %}
{% if index_td == 1 %}
{{ state_attr('climate.alex','temperature') | float(18)}}
{% elif index_td == 2 %}
{{ state_attr('climate.esther','temperature') | float(18)}}
{% else %}
{{ state_attr('climate.woonkamer','temperature') | float(18)}}
{% endif %}
temperature_cv_virtual:
friendly_name: "CV Virtual Temperature"
unit_of_measurement: "°C"
value_template: >
{% set alex_td = state_attr('climate.alex','temperature') - states('sensor.alex_sensor_temperature') | float(23) %}
{% set esther_td = state_attr('climate.esther','temperature') - states('sensor.esther_sensor_temperature') | float(23) %}
{% set woonkamer_td = state_attr('climate.woonkamer','temperature') - states('sensor.woonkamer_sensor_temperature') | float(23) %}
{% set max_td = ([woonkamer_td,alex_td,esther_td] | max) %}
{% set list_room_td = [woonkamer_td,alex_td,esther_td] %}
{% set index_td = list_room_td.index(max_td) %}
{% if index_td == 1 %}
{{ states('sensor.alex_sensor_temperature') | float(23)}}
{% elif index_td == 2 %}
{{ states('sensor.esther_sensor_temperature') | float(23)}}
{% else %}
{{ states('sensor.woonkamer_sensor_temperature') | float(23)}}
{% endif %}
Note that this is the old style as there was an issue getting the friendly_name to behave correctly in the new style. There is a long debate around this: Add (bring back) friendly_name to template sensors
But since the old style does not show signs of being decraped, i will use it like this 
Edit: i’ll mark this for future reference.