Hot water not very hot

Ectophile

The only reason it can heat the water that quick is a massive great gas flame.

The biggest kettle you can buy is 3kW. The smallest combi boilers these days are rated around 24kW. That's equivalent to having 8 kettles boiling simultaneously to heat the water.

daveyjp

This is also a good demonstration of why combi output should be matched to mains water pressure. Too low an output with too high pressure means no hot water.

Once the water is at temperature a modern boiler will modulate, it is very rare a modulating boiler will be on 100% burner.