presure at2.5bar all the time ?

worcester28cdirsf presure at 2.5bar all the time wether boiler is on or off, water trickels from relief valve all the time, when boiler is on its hot rustie water tried presure relief valve to reduce to 1bar but it continues to fill to 2.5bar.the fill key is removed it fills withot it in .please can you help