Not enough Hot water

Ok so here goes....

When taking a shower my hot water gets cold very quickly. I have followed the instructions on the front of the boiler mate 2 and calibrated the system, and all is working fine with regards to the green light being out after the boiler has stopped firing etc etc. And the central heating is working good.

When i had my shower today and the water started to get cold i slowed down the rate of water flow, and i then started to get hot water coming through again. But as soon as i opened the shower up fully again it just went cold!

I have recently had the gas flow valve and the heat exchanger changed on my Suprima 50 boiler. (not sure if this makes any difference?)

Also today i kept the hot water tap running and turned the Brawa mix valve fully cold and the water from the tap went cold. Then turned it fully hot and the water went hot. Does this mean that the fault isnt with the mix valve?

The hot water pump is set to speed 3 but doesnt seem to be moving that fast is this possible the problem?

The tank size is 120 litres

We have a new baby coming in 3 weeks so really need to get this sorted asap.

Any info would be greatly received.


Regards

Andy

Anyone want to help?

Seems that i have enough hot water for a shower as long as i slow down the water flow. But i do like to get blasted with hot water in the mornings!

Thinking its the pump thats the problem???

Andy