Periodic Airlock

[Onoff]

I've a cold water storage tank one end of the house that feeds a downstairs bathroom bath cold and upstairs ensuite basin cold.

 

It runs in 22mm from the cws tank then drops in 15mm to a tee. It runs in 15mm to the basin cold via a ball valve, it runs in 15mm to the bath via a gate valve.

 

Periodically the upstairs basin cold slows to a trickle then stops altogether.

 

To get the basin cold going I have to run the bath cold then shut it off at the gate valve after the tee then open the basin cold.

 

There's a stop end mark X just floating in mid air in the loft. If I put an air release valve there would that alleviate the problem?