If I have two electric showers ....

[Steve]

I'm curious - why would a correctly installed combi give a poorer output than an electric shower of merely half the power rating?

Because its an 18 year old Worcester 9.24e.

So what's preventing it from delivering 24kW?

The fact its ****. It probably does deliver 24kw, but its the way it does it that stinks.

The water starts coming out cold, takes about 1 minute to start hot. As the water gets hotter, it slows down to a trickle, have to keep turning up the flow. And it does just keep getting hotter, scaldingly hot. There appears to be no temperature or flow regulation on the boiler for the DHW. I just cant imagine it being any good for feeding a shower. No worries, its goin to the knackers yard next year.

 

[Goldberg]

I just cant imagine it being any good for feeding a shower. No worries, its goin to the knackers yard next year.

OK, so it's faulty. So in this:

It will give a better shower.

depends on the boiler, and if the shower is thermostatic. flow from my boiler slows down dramatically as it warms up.

... you were comparing a perfectly-functioning electric shower with a hardly-functioning gas boiler.

Getting back to the point, JohnD is quite correct in pointing out that a gas combi boiler completely outstrips an electric shower in terms of power output.