Combi Boiler output question

Sheepfan

We need to get a new combi boiler soon.  (previous Glow-worm was fine for the first 12 years but has become increasingly erratic recently)
Why would a 35kW boiler have a lower output for central heating than hot water?  This Ideal model has a 24.4 kW CH output, even though it's a 35kW boiler.  Is it an efficiency thing, and does it even matter?  
https://www.boilerguide.co.uk/productinfo/ideal/logic-max-c35-combi-gas-boiler

Ectophile

Because if your house really needs 35kW to heat it, then you desperately need to install some insulation.

Instantly heating cold water to hot water needs much more power than keeping a house warm, so there's no need for the boiler to run flat out when doing the heating.  Condensing boilers do work more efficiently at lower power.