What effect does the boiler temperature setting have?

[ericmark]

OK water too cool, and radiators can't put out enough heat, if set really hot, the DHW also gets too hot. But between the two extremes, what does moving that dial on the boiler do?

I understand how mark/space control works, but we have a boiler turning on/off, and TRV heads slowly opening and closing, and there must be a minium and maximum setting where ever that dial is set, and one would hope minium is higher than room temperature so the TRV can always cause the room to heat up while the boiler is running.

So how does turning the dial down help, why do we need an adjustment?

 

[Wayners]

Combi boiler has two dials.
Hot water and radiator temperature.

Don't sound like yours is a combi.

So dial on boiler is radiator temperature.
Hot water temperature is controlled in airing cupboard and if its really hot then thermostat maybe broken.
It's just going full on boiling water