Hi,
It is normal for the pressure to go up when the boiler is on. It wont be much noticeable when using the hot water as it is on for short period of time. You will see the bar going up when the heating is on as it is normally on for longer. However if the pressure exceeded 3 bar then you should see the Pressure relief valve discharging water where the pipe terminates outside the property. If it does discharge then you will loose all the pressure and will need to top up.

If the situation is where the Pressure relief valve discharging or the pressure goes up really quickly, this means your expansion vessel either require a service or it needs to be replaced.

Hopes this answers your question.

Thank you from Gas First Ltd

It sounds as though you are having a issue with expansion on your heating, this can sometimes be resolved by re pressurising your heating expansion vessel, if this continues after you have done this, then it may need to be replaced.
The vessel can normally be found inside the boiler or in a airing cupboard and is normally a red sphere shape.
Hope this helps.

As long as you’re pressure gauge is between 0.5-2.5 it’s no reason to book a engineer!
Do you’re annual service and everything it’s ok !!!

Depending on the size of your system you should have an expansion vessel big enough to cope (either 8L or 10L)the pressure inside the vessel should be between 0.7 to 1bar so if you top your pressure up to 1bar you should see very little rise ,obviously you are so you 100% have a problem with your expansion vessel