Mark,
I had the same issue. All my heater controls worked but no heat. I cleaned the heater core and is housing to no avail. I learned from SNG Barratt that the XKE heaters never worked well. I replaced the core with a new XKs Unlimited heater core and was amazed at the result. I now have heat - more than I need. I also know the heater controls work because I have to turn the heater valve off .
Stephan