to reduce combi boiler pressure

[rajantony1]

my 2 year old vailant combi boiler pressure sometime goes down , when u bring the pressure up it not staying in one place .it goes up up and all the way to full red i mean 3 t0 3.3 bar, is danger to the boiler or any problem please help me thank you

[The Builder]

Should be between 1 and 1.5 bar. Do you mean it goes up on its own, after you've finished re-filling?

[AlBags]

When you fill and there is a lot of air in the system, it will rise pretty slowly. However, when all air is expelled, the pressure will rise really quickly when you are charging it.
You need to fill to about 1bar COLD when all air bled out. Check again when hot. It should not really be over 2bar. This depends on system size, but average system.
If it IS, get the expansion vessel removed and checked .. It may have failed (diaphragm inside) either from old age or constant over-pressurising)