Improve hot-water flow rate to new shower?

[Jukes]

Hi All, I am a complete novice after a little bit of advice from one of you experts please?

I have just had a new shower fitted in my ensuite upstairs and wanted some advice on any simple, cheap ways to improve the water performance?

Brief details:

gravity fed system

thermostatically controlled shower valve with 200mm square shower head (ceiling mounted)

shower pump 1.5 bar twin impellor (positioned in loft)

If I turn the heat dial on the shower valve to full cold I get a great water flow rate, in the default setting the water isn't very hot and not very good flow-rate. When you turn it onto the hot side it is nice and hot but very weak, almost dribbly.

I'm sure the best solution is to replace the boiler as it's a gravity fed system and apparantly not really very good with modern showers? (it's over 10yrs old) but I was wondering if there was any other simple ways to give an increase in the hot water flow-rate?

• Would changing the fixed shower head for a smaller one, like 125-150mm (current head is 200mm sq and has 100 water nozzles, would a smaller one with say 50-60 nozzles make any difference?)
  
• Would increasing the amount of time the boiler heats the water every day make any difference?
  

Thanks in advance.