No Heat 1999 Deville

Had no problems till this am. Everything seems to be working added fluid to reserve tank it was low cked hoses at firewall and felt them they were warm. When I play with the climate control buttons I get some warm air very briefly thru dash panel vents but otherwise cold to floor etc. Any help would be great. Thanking readers in advance.

First check your temperature gauge (if you have one), check to see if if the gauge reads less than the middle of the gauge during normal driving and moderate outside temperatures.
If it does, replace the thermostat and radiator fluid. The thermostat is probably not opening and closing when it should. This is a cheap repair and is likely your problem.

I am getting codes 1340 and 1341 air mix door movement fault. I am not sure if I have a temp gauge but I will ck into it. Do u think the thermostat has anything to do with the air mix doors? I would much rather replace that then tear ny dash apart? ugh Would all my hoses still be hot if the thermostat was not working properly? Thanks for ur advice