All this hot/cold water pressure combi boiler stuff.
In my old flat the hot water flow rate was a fraction of the cold. Reducing the heat to increase the flow was counter-productive because you needed less cold water mixed into the shower. Increasing the heat to 'rather too hot' reduced hot flow rate even more, but you needed more cold to bring it down to acceptable temperature which meant that the shower pressure was better. It was also the only way you could fill a bath at a decent speed, cos you mostly used the cold tap.