IMM wrote:

Why do you say the combi provides a
constant temperature?


It has an output thermostat attached that modulates the burner to suit.

IME the stat will prevent the boiler exceeding the maximum selected
temperature. However, there is nothing it can do once the maximum heat
output of the boiler is already demanded. For DHW at 60 degrees this
will be at quite modest flow rates even on high output combis. The
result is the DHW temp will fall (and by a large margin). ISTM that a
thermostatic mixer will be able to take account of a large swing in
output temperature from say 60 down to 45 by varing the cold input from
"some" to "practically none" - I can't see how just balancing the
pressure alone can achieve the same result.

How does the pressure balance cope with that?


If you are drawing 8 l/min and then taps are turned on to ramp up to 14
l/min, then the pressure in the hot line will drop. The balancing valve will
drop the cold inlet to the mixer to the same as the hot, preventing
excessive cold being drawn off through the mixer, keeping the temperature
stable.

but that does not take account of the fall in the DHW temperature that
accompanies the pressure fall - if you are balancing only on pressure
you must assume a constant (ish) temperature supply of HW.


--
Cheers,

John.

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