--how many rads you have is nothing to do with hot tap temp.--              --you should never fill a combi to 3 bar you will activate the prv, if you have 2 or 15 rads.-- 
fill the system to 1 - 1.5 bar max  just don't let it drop below about 0.7 bar.
 poss faulty dhw thermistor.
                        (don't take up plumbing)
                
 hi-spec plumbing
                
 March 2007