the manual states for my ferroli modena 80 that the hot water flow is 9 litres/min.am i correct in thinking that if i measure the max flow rate from the hot tap it should be close to this.if i run a bath and turn the hot water tap on in the kitchen at the same time then no water comes out the kitchen tap.

9 lts per min is the lowest flow rate from most combi's, flow rates vary between boilers and manufacturers from 9-18 lts per min. With only 9lts to start with then running 2 taps at once is unrealistic I'm afraid.

Mog