Me too! I have an RD532i that goes from 1.5 bar to almost nothing . Did you ever have it diagnosed and fixed?
My other researches on the web suggest that this symptom could be related to a problem with the boiler's expansion vessel (whatever that is!), but I cannot find any data on how to fix it. I don't even know if this is something that I could/should try to fix myself, or whether it needs a trained gas fitter to do the job.
Any advice would be very welcome.
Hugh
November 2010