We have a combi boiler which is approx 9 years old. Recently we have had a lot of problems with it, but thankfully we have boiler cover with British gas, so they have been out to fix it. We have had a new dhw hear exchanger fitted, prv, dhw sensor, and I thought a new diverter valve, but can't see that on the paperwork. It has also been serviced, and they have said it is working at 88% efficiency. Now, it has another fault. The pressure has now dropped to just over 0.5 bar(it was at 1.5 bar after last visit on 9th May). It now makes a whining noise when the hot water is running(the boiler is now set to hot water only, so heating is off). The noise doesn't happen straight away, but after a couple of minutes. I'm no expert, and have looked online, and was wondering if this is a sign of the pressure vessel being on its way out? Any advice would be greatly appreciated.