Vokera Linea 24 hot water temperature anybody?

Need some advice on our vokera linea24. Had a proper look in manual,but can't find all answers.We have a pretty common problem,I gues,by what I found on different forums.Fluctuating DHW temperature.Pressure is fine,don't show any errors,checked and cleaned all valves etc.Just seems to go cold now and again when hot water is in use (shower etc), no way for it to cope with two taps on at one time either...Temperature shown on display is roughly 47,but seems to be clicking off too soon instead of just lowering flame.In book it says that water temperature is around 80C, I understand that would be tempereture circulating around,before it goes back again to heat exchanger.Or is it that it circulates too much round boiler and don't feed out enough?Taps seems to have good pressure,so don't think it's that.What is an average DHW temperature that will come out of taps?What can I expect?
Thanks

Magdalena
February 2009