Maarten

Ive done exactly this. Using my Pow R2, bought one of these temperature sensors https://www.diyelectronics.co.za/store/temperature/297-waterproof-temperature-sensor.html?search_query=dsb18b20&results=1.
 
Then soldered it to the pins exposed on the board. Used ping IO4 (do not use IO5 as it is connected to the power measuring chip and it will damage it, i know :P). Extended the probe cable with alarm wiring, as they are thin and cheap. I think you can go max 10 meter. Attached the probe next to the thermostat against the tank side wall thing.
 


 
Using following esphome code
 
On home assistant you then get

and

Ive done exactly this. Using my Pow R2, bought one of these temperature sensors https://www.diyelectronics.co.za/store/temperature/297-waterproof-temperature-sensor.html?search_query=dsb18b20&results=1.
 
Then soldered it to the pins exposed on the board. Used ping IO4 (do not use IO5 as it is connected to the power measuring chip and it will damage it, i know :P). Extended the probe cable with alarm wiring, as they are thin and cheap. I think you can go max 10 meter. Attached the probe next to the thermostat against the tank side wall thing.
 


 
Using following esphome code
 
On home assistant you then get

and