No heat after engine is warmed up

I am not an expert , but I have had similar issues,My first suggestion would be to check your fuses,Next thing that could cause low to no heat output could be your thermostat froze up, or in some cases I have seen them completely removed to try and remedy a car running hot .

"Burp" the system to remove air from the cooling system. Utoob has videos.

Thermostat is stuck change that first if not that look at your thermostat control on your dash and if it's working properly it could only be one other thing that I know of your heater core is stopped up or has been bypassed if it's bypassed your heater hose comeing from water pump will just loop right back to itself and we're hose come out of firewall on passenger side might be looped back to itself also just a easy way to check without any work but if all that is working and all I've listed above isn't any problem I would say u might have a sensor or bad waterpump if it's waterpump take flashlight and crank care put on ramp and crawl under car and look at underside of waterpump there should be a weep hole it should push enough water to drip or even pour out if it's bad and also it still could be bad even if it doesn't leak from weep hole just some simple ways to check without actually taking car apart most of time its thermostat or sensors then I would check heater core and then water pump and if all else fails drain your radiator if it's not mostly antifreeze u. Could have a circulation problem water flows faster than antifreeze and does not cool or heat as well in extreme weather conditions such as cold you will see people with cardboard or even grill covers to block the cold air from over cooling the coolant in radiator but good luck and let me know if u got it figured out god bless