Instant hot water via electric heater without expansion tank

[kez1]

Hi,

I just installed a
Galaxy GAP95 Powerstream Unvented Instant Water Heater 9.5kW
( www.screwfix.com/p/galaxy-gap95-powerstream-unvented-instant-water-heater-9-5kw/93177 )
to supply us with hot water to a sink with one hot water tap only. The tap is not a mixer.

It does work though we have to turn the flow down to a very meager flow rate to get really hot water.

When the sink hot water tap is fully on I would say that we only get 1/4 of mains pressure, which is what the device supplies as output ( the device mains input pressure is not restricted in any way ).

Can anyone recommend an electric system that does not need an expansion tank that produces very hot water at full mains pressure ?

( ... and would the Galaxy 12kw make a big difference .... )

Thanks

Kez