If you look underneath the bottom of the boiler there should be two tear shaped levers, one on the right hand side, the other more towards the front right of center, open one then the other and recharge the pressure to between 1-1.5, I would suggest you chech your system for leaks, especially around the rad valves,and the pressure relief pipe outlet which should be located outside roughly level with the bottom of the boiler.
gary.wright53@googlemail.com, June 2007