--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