HI Guy & Girl
Just thought I would give some info for those with the same sort of problem !!
Bought the XM a few weeks ago the auto setting on the heater was not working
I just got round to fixing it very easy repair
In the roof light is a sensor that tell the temp to computer this gets blocked with dust Etc stops the fan inside the sensor from working
If you remove the light 4 screws under plastic cover the sensor is the black thing near the back of the light remove un clip the wires and remove sensor
Clean with a paint brush and spray with switch cleaner
Plug back in to make sure it is working fan should spin if not replace with new one
then replace
The biggest give away when it needs doing is a wearing noise coming from the light area when you first turn the ignition on sounds like it is running on steam
Take it out and clean it
Well I hope this will come in use for someone
TTFN