If there is a constant or regular drip from the boiler, that will make the pressure go down eventually. Just be sure the pressure isn't going up to 3 bar while heating, as that would indicate a faulty / uncharged expansion vessel combined with a bad connection of the PRV to the PRV outlet pipe. It could even be a faulty dripping PRV, and the outled pipe not attached properly so it drips from the boiler instead of the outside pipe.
Whoever you employ to sort it out, tell them you know nothing about boilers, tell them you will pay them to fix the leak / drip / pressure loss and that's what you are paying them to do, whatever they have to do. That way, if they come, do stuff, charge you for fixing it and the fault persists, then they are obliged to return FOC and sort it out.
Whoever you employ to sort it out, tell them you know nothing about boilers, tell them you will pay them to fix the leak / drip / pressure loss and that's what you are paying them to do, whatever they have to do. That way, if they come, do stuff, charge you for fixing it and the fault persists, then they are obliged to return FOC and sort it out.