DC 18 intermittent brush beater (Solved)
The fault was the cable loom for the cleaner head.
The brown wire had broken and only made contact when the Dyson was closer to the vertical than the 45 degree or more convenient cleaning angle. The blue wires insulation was starting to crack and pulling on it at that point caused the insulation to stretch showing that the copper wires were down to a few threads.
Until I saw the replacement part online, I thought the lead was just straight piece of wire that was fitted on a Friday afternoon by a tired assembly worker who unwittingly had kinked it causing a weak point. The wire is covering is hard reducing its flexibility.
However, the replacement part viewed online has a coil towards one end that seems to aid flexibility.
Therefore, I now do not know what to think as my wire shows no hint of four coils that the replacement has.
Was my wire straight and fitted with a twist and the manufacture has spotted their error?
I must thank markcorrado1 https://manchestervacs.co.uk/DysonForum/index.php/topic,408.0.html
for his tutorial on how disassemble the undercarriage assembly with specific thanks as to how to remove the plastic cheeks (Wheel caps) not knowing this I nearly wrecked them trying to lever them off. It is the knowing that you can apply enough force with just your fingers that gives you the confidence to do it!