Central Heating Water Hammer
 

I have a sealed Y-plan oil-fired system that was upgraded from a gravity HW,
pumped CH in the last year.
I now find that, having successfully removed all the air from the system by
adding a separator, there is a brief second of water hammer when the 3-way
valve changes its position. This happens even when the pump, Grundfos Alpha,
is at its minimum setting.
What I would like to know is: will I solve the water hammer issue by
changing to an S-Plan system using two 2-port valves instead of the 3-way
one ?
Perhaps a shock arrestor maybe the answer ?

Thanks

Alec