wrote on Apr 22^nd, 2012 at 12:12am:

if i turned the flo-rate down, i would have to run around in the shower to get wet. i'v got most of the filters out and it seems to be working a little better,cos the weather is warmer, :) truth will tell when the water is cold from he supply.

So you seem to have two problems.  Insufficient temperature out of the boiler and insufficient pressure.  What is the model number of your Ariston heater and how are you deriving your pressure (head or pump).  You're right that if you're struggling now for temperature, you'll definitely have problems in the winter.