Invented system

[David2749]

I've a unvented system which has just been serviced, the guy dismantled the water pressure valve to check the mesh, which was ok. Prior to service, when I turned the hot water a hammering noise came from Near the tank . The guy said the noise was probably the valve but would be ok. Well to me that's not ok.
There isn't any water coming through the tun dish.
Any suggestions

 

[Silentrunning]

In my previous house I had water hammer problems. I put an air tank at the end of the plumbing. This worked as an accumulator.

 

[David2749]

It's not the usual water hammer noise.
When I turn the hit water on , the water pressure is high, that's when the noise starts, after a few seconds the pressure drops as does the noise.
I just want it resolved, that's why I had it serviced. But it still happening.