You can bleed a radiator into a tub to lower it
Does the pressure rise on its own?
Is it only when the heating is on?
It only happened this morning when the heating was on. After an hour the pressure went down to nearly into the bottom area of red.
Thanks for the suggestion of bleeding a radiator.
If you refill the system back to 1 bar when cold, but the pressure rises dramatically then you will need someone to look at your pressure vessel, as this is the part that takes the expansion when the water is heated.