Decided to bite the bullet and try to fix the problem.
Seal kit obtained from plumbase.
Had already obtained replacement instructions direct from Mira (visit their website, very helpful people).
Needed heat to get cover assembly off along with large stilson wrench and a hammer.
Replaced all seals and put it all back together and guess what? still no hot water coming out when shower head lifted up.
Needed to replace seals anyway as there was a leak.
Removed shower head and held hose in the air, hot water came out when fully hot selected. Cleaned shower head holes with a pin. Tried again, hot water Hurray
Tried shower myself first in case of any problems, felt great.
Hope this may help any readers.