Re: Not for brits
@ Gordon 10
> firstly I don't shower at the time someone is doing the washing up.
Lucky for you, some do.
> Secondly most modern high flo combi's solved that problem years ago.
Only by using ever higher power outputs - ie installing boilers that are grossly over-sized for what they do most of the time. I did measurements in my flat after fitting a thermal store ...
With daytime temperatures hitting the heady heights of "not still freezing" the flat took an average of about 2kW total to keep it "comfortable". The combi (which now is only used as system boiler to reheat the store) is nearly 30kW for a p**s poor flow rate (start filling the bath, go back and watch telly, and hope it's filled before it's gone cold) - with (for this model) a minimum range of just under 10kW. So the boiler (on minimum output) is around 5 times oversized for average load when heating. Yes, modern boilers have got "better", but they are still crap compared with a decent stored heat system.
@ Jon 37
> Thirdly - get a thermostatically controlled mixer shower, then when someone turns a tap on the shower stays the same temperature, but the flow might reduce a bit.
A bit ! Try "down to a dribble if you're lucky".
> Getting your heating engineer to install a boiler that will give you hot water at mains pressure in the shower while your dishwasher *and* washing machine run is not always easy, but it's better in the long run.
No, it's a darn stupid idea. You'll have to fit a huge capacity boiler, it'll cost you a fortune (capital, maintenance, and running costs) compared to one that's even vaguely sized to the heating load, and it'll be somewhat inefficient when running the heating.
A 30kW combi will still only give you a "modest" flow rate, but unless you have a big house it will be well oversized for the heating. If you do have a big house where a boiler that ranges down to perhaps 8 to 10kW is suitable, then your house is most likely too big (too many people) for a 30kW combi.
> Or get an electric shower.
Then you can imagine what it feels like to have someone stand over you and give you a "golden shower" such is the flow rate vs temperature trade off. Most combi boilers are around 30kW and upwards, which is enough to run a decent shower and (with care) a small flow from one tap. Most electric showers are in the "up to" 11kW range - with many significantly smaller.
Something else while the subject is efficiency ...
While there's the same "flushing the cold water out of the pipes" wait as you get with a stored heat system, with a combi you get either another delay (so wasted water) or wasted heat. At the same time I did the measurements in the flat, the house next door was empty so I could do a direct comparison. With the heating off, and no hot water being used, the combi in the house (a fairly modern one) used TWICE the energy keeping itself hot and ready for hot water as was lost from the thermal store in the flat. That's with the boiler firing up from time to time to keep the DHW heat exchanger warm - yes you can put it in eco mode and stop that, but then it takes longer to produce hot water (you can even buy an (expensive) valve designed to restrict the hot flow until the boiler is hot to mitigate this wastage of water while waiting for it to heat up.
Summary - combi boilers are expensive, complicated, unreliable, and inefficient. When, not if, they break down then you are left with no heating or hot water - unlike flipping on the switch to use the electric immersion heater a stored system allows you to have for backup.
But builders/property developers love them because it allows them to shave about 1 square meter of the space needed in a dwelling.