Bolier pressure - Central ceating issue

[MrDave]

Hi,

I noticed the pressure this morning on my boiler was just below 1bar so I went to top it up, opened the loop and it just managed to hit over 1bar then just stopped increasing.

Now the central heating looks like its on but all the radiators are luke warm even when temperature is 70 degress +

Boiler is a Logic Combi ESP1 35

Any ideas what this could be?

Thanks in advance