Y plan system - boom when pump operates for rads during hot water schedule

[craig1234]

I have a Y Plan heating system and there is a "boom" during the hot water schedule when the heating side calls for heat. My understanding is that this is caused by the pressure of water against the valve when the pump initially starts up.
My question is, what is the best way to overcome this?
Thanks

 

[Madrab]

Usually down to a poor quality or lazy/tired valve and it's the ball banging against the seat when the motor switches to mid pos and the system is already running/flowing. Y plan's or rather the mid pos valves are notorious for causing problems/getting noisy when they get older and tired.