have you tried balancing the heating system ? so that the hot water is evenly distributed to all the radiator.
Water at kitchen tap is too hot ? what about bath tap and wash basin ?
Remove a radiator and flush, if there's sludge building up - then yes a powerflush may help. If the water is clear or not too bad then a flush wont do anyhting.
If the central heating is pumping over then you need to look at the pipework and the position of the pump. Has the pump been changed or pump speed adjusted ? try turning pump speed down and see how it works.
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