While my PRV gently weeps...
QThe pressure relief valve on my calorifier seems to constantly weep when the water is being heated via the immersion heater when I am connected to my shoreline power. Could the PRV be faulty?
Whenever cool water is heated it expands. The accumulator should take care of most of that by providing a space for the water to expand into without raising the pressure to a significant degree. If there is no air space (air is compressible, water is all but not) in the system and you have closed taps, the pressure in the system will rise very quickly and cause the PRV to dribble, this is normal for a boat with no accumulator or expansion tank.
You could try fitting another accumulator on the hot side of the calorifier pressurised to 1.7 bar so it acts as an expansion vessel. If you fit a PRV of a higher pressure than that recommended, you stand a fair chance of splitting the calorifier by pressure from the expanding water.
Once you are sure the accumulator is pressurised as I indicate, the next thing to do is to fit a new PRV set to whatever pressure Surecal recommend. Some have a rubber washer like a tap washer and this can go hard.