Finally got a dometic agent. Theromstat is located too low on wall. Warm air outlet was bent into a nice "S" shape through the underbed storage divider. The cover over the heater was installed too low. The end result is a heater that overheats and turns off.
So a bit of work today and the warm air is now in a straight conduit and the cover is raised by 100mm. Hopefully this cures the issue.
The repairer installed a new thermostat and switch in a better location
Old outlet on the rhs, new one on lhs.
You can see the old hole for the outlet through the under bed divider. So the pipe did a fairly tight "S" bend to get to the old outlet.