Cavitation in honeywell 3 port valve V4073A

[boilerbloke]

Having just fitted my HW/CH system with new programmer and 3 port valve( honeywell V4073A fitted on the flow) all working fine, except I get bad cavitation noise inside the 3 port valve when it is in the AB mid position feeding both HW and CH. I have tried turning down the speed of the pump (which is on the return) and this does help, except it is not strong enough at low speed to pump to upstairs rads.

What can i do to stop the cavitation inside the valve
All is fitted correctly according to specs.

Is the valve faulty? is it the wrong type? Does the pump need to be on the flow?
Do I need a valve with a higher differential pressure?

any help welcome please.

Thanks
Paul

 

[weareleeds]

Best place for pump is on flow with cold feed & expansion close coupled next to it. You don't have self priming cylinder do you as it is unusual for pump to be on return

 

[boilerbloke]

What do you mean self priming cyclinder?
My cyclinder fills itself from a header tank. open vented

Do you think having the pump on the return is causing the cavitation?