My 2000 XK8 runs at good temperature, blowers work fine,gauges all fine but stopped blowing hot recently no matter what temp i set it to

 

Check this earlier post: heaters-not-working-219285/#post2087083

 

On the firewall in front of the driver there is a valve which allows hot coolant through the firewall for heat. The valve is spring loaded open and closed electrically when the air conditioning is turned on to keep the hot coolant out when you don't want heat. If the spring breaks and the valve happens to be closed, you won't get heat. Once you select air conditioning, the valve will be commanded closed electrically and that's probably where it will stay because there is nothing to open it.
I had the opposite problem for a while. The valve wouldn't close, so I always got hot air no matter what I selected. A calibrated blow to the top of the valve set it right and it seems to have gotten the message because I haven't had the problem in years.