Worcester Bosch 40CDi - Fault Code 5E?

I have this code 5E flashing on my display.

Other answers suggest it is a servicing scheduling problem, but my boiler was recently serviced on the annual contract just before Christmas ready for the winter, (its only the end of March now).

I have had cause for concern lately because the pressure has been dropping gradually. I have topped it up when it has dropped to below 1 Bar and I have checked all the radiators for leaks and have bled them several times over - they are all OK.

I have had it suggested that there may be a problem with the Pressure Relief Valve (PRV), (whatever that is).

Should I be worried? What should I do?

It is Easter weekend and getting someone out to look it over will be almost impossible until next week, so what should I do?