Can you post a photo like the one in post #9. What does the display show if you press the "Mode" button?
"The only thing I can adjust now for central heating temp now that the WC is fitted is the slope setting between 5 - 35."
This is NOT the slope, its the room set point, RSP, the slope I think was 1.4, this is the one I would suggest increasing to say 1.8 or even 2.0 and leave the RSP room set point at 20C, initially, this will raise the boiler flow temperature.
"The only thing I can adjust now for central heating temp now that the WC is fitted is the slope setting between 5 - 35."
This is NOT the slope, its the room set point, RSP, the slope I think was 1.4, this is the one I would suggest increasing to say 1.8 or even 2.0 and leave the RSP room set point at 20C, initially, this will raise the boiler flow temperature.