Combi Boiler Pressure Dropping - Re-Filling Most Days

[MANDATE]

Both issues need dealing with!
You don't say where on the valve it's leaking from.
Could be a compression joint ( undo and use sealant or ptfe tape on olive)
Could be valve spindle (tighten a touch or undo gland nut and wrap ptfe tape round spindle.
Could be thread on the radiator tail (may need removing to use sealant or ptfe tape to make good the joint.

The PRV needs either cleaning or replacing.
You need easy access and special 'C' type spanner to remove the head to clean it.
It's easier to remove it and replace with a brand new one.

 

[cwcw]

Well, after the first day of around 200ml leaking out of the PRV, very little if any has leaked out in the last 3 days, but I still needed to top up in that time.

The TRV that I took off won't screw back on, or at least I can't work it out. It had a fresh leak from that radiator last night, but only a penny sized puddle. The other leaky radiator is dribbling very slightly from the top of the valve. Both radiators drip, or drip more, when the heating is off and they cool down. When the heating is on, the TRV one doesn't leak at all, and the non-TRV valve one leaks a lot less.

It could be time to get the plumber back and discuss the findings. I hope this is enough to go on.