Hot Water Pressure with a Combi

[MarkClarke]

I have just had a new COMBI boiler fitted (Worcester Greenstar 35 CDi) which I am very,very impressed with it is soooo very quiet and the heating comes to life very quickly. I do have a small concern and that is that the hot water pressure is not as good as when I had a cylinder type system (This had a 1.5 Bar pump installed).
The flow rate from the cold water main is well over 17 litres a minute and the pressure is about 2 BAR, this boiler I believe is capable of 16 + litres a minute, is there any way I can pump the water to get as good a shower as I used to have.
Thank You

 

[ChrisR]

No, sort of. It's FLOW limited to keep the water hot enough in the winter for a bath.
You could get the flow limiter taken out but 2 bar isn't that high, so I doubt you'd get more water through it, and it would be cooler...

What flow of hot are you getting?

 

[simond]

Chris R is right; you cannot achieve a higher hot water flow rate than the Greenstar is capable of; if memory serves me this model it is about 14l/m (I think the 40CDi does around 16l/m). Their www site will confirm.

If you water main is delivering circa 17l/m we would not have specced the 35CDi because you would be unlikely to see it ever running full bore - normally people mix in cold at the point of use at the ratio of between 1:4 or 1:3.

However, most shower heads can only deliver around 10 litres per minute, I assume that you haven't got a 'drench head' in there which can do 20l/m.

If you have a normal head and the pressure is drastically falling off as soon as you open the tap, you could fit a water accumulator on the mains supply to give a more consistent pressure.

As things stand 2 bar static pressure is good but if the water main is restricted in diameter this will fall drastically as the flow rate is moved between 0 and 17l/m. Therefore once you get to 10 litres the pressure might be abysmal compared to your old shower pump.

If you have a drench head your options are altogether more limited and a combi is not a good match for these products.