fitting new heat exchanger?

i would suggest common sense tells you if you can get hot water from one tap it can't be the heat exchanger otherwise you wouldn't get hot water anywhere use a measuring jug to check flow rate of taps (about 9-10 ltr per min depending on boiler) give the water enough time to reach temperature you may simply be running the taps too fast ok in summer but not in winter

brian
December 2010