The heating has been off now for 10 hours and the gauge indicates 1.25. I suppose it's ok now?
As an FYI, hot water expands.
Therefore the pressure will drop when the system is cold and it will increase when the system is hot.
As long as it remains within the green zone you are fine.
If there is a small leak it may take quite a while to prove (weeks) as a pinprick leak may only happen when the pressure is high/hot and it may take a week or to before you notice the pressure drop.
Also as water is circulated around the system the oxygen is slowly removed, it will collect at the highest point, (an upstairs radiator?) which will need bleeding, which in turn will mean you will need to top up with water for the air you have removed