losing pressure

Hi guys I am really hoping someone can help me here. Quite a lot has happened to get to this point, so please bear with me. This boiler was already installed when I bought my house and it has served me well in the 7 years I have been here (it was installed 14 years ago) - I have had it...

I have a Grant Vortex 26, and it is losing pressure. It can be at 1 bar in the evening, and be down to 0.3 bar in the morning. When the heating is on, it holds pressure, but as soon as you turn on hot water somewhere in the house the pressure drops. I thought the two systems were separate, but...