I write this topic to help you decide if you want the "external sensor" (+ 15 EUR, +10 EUR bought as a bundle)... To avoid confusion: the FGT-001 does only displays temperature if you add the external sensor. Without the sensor, it displays "--". But that is not the main reason to buy one... You might have heard the TRVs cannot measure temperature accurately, because their sensors are "not in the right spot". But the question is... how bad is it? I encourage you to have a look at the setup, the