Got to be the stat then buddy, even though it's a new one they can still stick either shut or open but in this case sounds like it's shut and not opening on temp

Fair play buddy, hope it works for you

Daft question but the belt is in tacked I presume?

Sounds like the pump is not either turning correctly to deliver the correct water pressure or it's even siezed not giving you circulation that's why your not experiencing air in the system

Hi all just joined the forum so a little slow until I find my feet, I've just bought a td5 90 defender which has been my dream for years