Hi, This is my first post so hear go's , I have a Riello Atos Fuel BR 35 wood burner (5 years old) with the Viessman 200-h . At the moment we are having outside temp of -6°C and I cannot boost the heat from around 20° C as I would like 25°C . I have underfloor heating . Any advice would be great, thanks in advance. Regards Michael