Is it an airlock or debris in pipes causing issues with kitchen and bathroom taps

[grekko]

I have a continual problem with my bathroom and kitchen taps hot water flow.
I have hot water and central heating run from a condensing boiler to copper cylinder in storage cupboard.
Every couple of days the hot water flow in the bathroom almost disappears completely but still flows,at a reduced rate,in the kitchen whereby I then have to force mains cold water up the hot pipe to restore the flow. Unfortunately, this eventually leads to an overflow from my storage tank in the attic to the exterior of the house. I then have to drain down half of the storage tank and wait maybe another 5 or 6 weeks of forcing the cold water up hot pipe for the overflow to return . Can anyone tell me if this problem is an airlock or a debris blockage in the piping somewhere or is it another cause ?
Thanks in advance .

[grekko]

I have a continual problem with my bathroom and kitchen taps hot water flow.
I have hot water and central heating run from a condensing boiler to copper cylinder in storage cupboard.
Every couple of days the hot water flow in the bathroom almost disappears completely but still flows,at a reduced rate,in the kitchen whereby I then have to force mains cold water up the hot pipe to restore the flow. Unfortunately, this eventually leads to an overflow from my storage tank in the attic to the exterior of the house. I then have to drain down half of the storage tank and wait maybe another 5 or 6 weeks of forcing the cold water up hot pipe for the overflow to return . Can anyone tell me if this problem is an airlock or a debris blockage in the piping somewhere or is it another cause ?
Thanks in advance .

ADDED PHOTO OF MY CYLINDER CUPBOARD..I'M AT A LOSS TO ]UNDERSTAND THE PIPE WORK

[lets have a look]

A couple of thoughts,because it only happens every few weeks makes it difficult to diagnose, first make sure there's a good flow of water into the cold water storage tank,that's the first thing, I notice that the tee from the the top outlet of the cylinder isn't visible,it should preferably be at the top of the cylinder,the pipe is a vent and the branch on the tee takes hot water to the taps which can cause airlocks if situated near the ceiling or in the attic.