o The CH doesn't work, and that's because the water pressure is too low (0.4 bar, the cut-off point on my system).
o Repressurising to 1.0 bar fixes that, for day or so, then the same thing happens once the system cools down.
o There are no interior leaks, but today I noticed the pressure relief valve was letting out water. The water pressure was 3.0 bar at that point.
I don't think it's suffered from overpressurising in the past (so that the relief valve would open and get clogged). So what would cause the pressure to rise too high? (Presumably the pressure relief valve is operating correctly.) The expansion vessel? When I checked the air pressure a year or two ago, it was exactly the same as the water pressure; which sounds about right...)