2002 xkr heat stopped working. It only blows cold air. On a 45 minute trip it never got hot or even warm. During the winter it was working fine

 

My prior car, an '01 XK8, had something similar.

Every now and then, mostly on the 1st call for heat in the Fall after a summer with no use, it delivered only cold air.

By trial end error ... setting the temp control to max and letting it run there for a few minutes made heat, and then the temp control could be set where I wanted it. No idea why this worked, but there it is.

 

Check the heater pump fuse (#15, 10 Amps) in the fusebox under the hood on the driver's side.

If that is OK you might also try swapping the relays in the fusebox.

If still no luck, either:

-Your heater pump has failed
-Your heater core is clogged
-Your heater valve has failed
-The electronic controls have failed.

The heater pump is most common, but coolant types were ever mixed in this vehicle a clogged heater core could be a likely result. The valves do also stick occasionally.

Plenty of info on most of these repairs on the forum.