Just keep the PRV open, as you say it can't make it any worse.
Once you have charged the vessel correctly (0.8bar) and water pressure set to 1bar afterwards the rise in pressure when heating is on should be about 1bar.
The problem then transfers to the PRV. If any sediment is trapped between valve seat and washer, there is going to be a small leak and you could lose pressure regardless of whether the heating is on or not.
For example heating is off at midnight pressure 1bar. following morning pressure dropped to 0.5 due to PRV.
Its one of those situations where one problem creates another
Once you have charged the vessel correctly (0.8bar) and water pressure set to 1bar afterwards the rise in pressure when heating is on should be about 1bar.
The problem then transfers to the PRV. If any sediment is trapped between valve seat and washer, there is going to be a small leak and you could lose pressure regardless of whether the heating is on or not.
For example heating is off at midnight pressure 1bar. following morning pressure dropped to 0.5 due to PRV.
Its one of those situations where one problem creates another