In this video I build a sensor to monitor the flow and return temperatures of my boiler using ESPHome running on a Seed XIAO ESP32-C3 and using two NTC thermistors to measure the temperature.
If you have a condensing boiler, it can be useful to monitor the return temperature to ensure it never goes above around 50C as that will stop your boiler condensing and reduce its efficiency considerable!
I’m using thermistors instead of the usual DS18B20s as I found you can buy them built into a clamp, making them far easier to install!
Watch on YouTube - Building an ESPHome F.A.R.T. sensor for your boiler https://youtu.be/hC5STZaQ3CE