On arrival at the property it was obvious as to what the problem was.
Looking up at the Aerial before knocking at the door it was clear to see that this TV Aerial was missing a quantity of it's elements, later my customer did admit that he had not looked up at the TV Aerial prior to calling me.
As a general rule of thumb the more plastic used in the design and make up of a TV Aerial the shorter its life will be. This Aerial made by Diamond Colour is a common example of the problem.
I often see TV Aerials which are missing one or two elements, surprisingly tho there is often little or no significant drop in signal strength but this does very much depend on which elements are missing, in this particular example the Aerial had lost 5 elements and because of their position relative to the Aerials dipole those missing 5 elements dramatically reduced the Aerial's ability to deliver a sufficient signal to the TV.
The plastic parts of a TV Aerial are often the parts of a Aerial that fail first with the UV light from sunlight being the catalyst. Over time the UV light makes the plastic brittle and crumble allowing the aluminium elements to come loose or fall from the Aerial's boom.
In this case a poor design regarding the attachment of the aluminium elements to the Aerials boom via it's flimsy plastic insulators/holders was to blame.
This Aerial was only 12 years old whereas a good quality, well installed TV Aerial should last in excess of 30 years.
The TV Aerials I supply, install and recommend contain less than 1% plastic material in their design with an expectant life in excess of 30 years.