ᐅ Underfloor heating – Return flow warmer than supply?! What to do?

Hello everyone,
A few quick facts about our single-family house:
- 157 m² (1,690 sq ft), detached
- Guntamatic pellet heating system
- basement included
- KFW 55 standard
- heating curve 0.5
- moved in November 2018

Which parameters should I adjust first if the return temperature is higher than the supply temperature?

Hello
This shouldn’t actually happen when the boiler is running (generating heat).
Do the measuring points show the correct temperature?
Is it possible that solar-heated water from the buffer tank is flowing to the boiler?

Olli