Hi, I'm looking for some advice regarding a Worcester Bosch Greenstar Heatslave 18/25 oil boiler. It's been installed around 18 months and it's started to slowly lose pressure. Until today that is when I turned on the hot tap to wash my hands and the pressure gauge dropped a notch. A little while later I washed up and the pressure gauge dropped another notch. During both these times the boiler wasn't actually on as the hot water is on a timer and hadn't reached the switch on time. Can anyone explain why the boiler did this? I've checked the rads, pipes ceilings for any signs of leaks and nothing and there's no water under the boiler or coming out of the vent pipe outside so I have no idea what's going on!! Thanks