Check the fluid level in your radiator. A low level can cause this. If you have checked your fluid level and everything is still not OK, then I suggest you change your heater block, it may be blocked or damaged.
I agree it is probably the heater core. It is located behind the dash on the passenger side. This means it will be a fairly long process( removing the dash assembly, etc.). High labor cost at a shop for a $100 part. There are numerous guides online if you feel up to the task.( Google search: how to replace a heater core in a Jeep wrangler) probably a weekend project.
Heater works fine in my Wrangler! Check the thermostat or the hoses or heater core might be plugged. The thermostat is easiest ^ cheapest to change so start there.
Try flushing heater core Try flushing heater core
How did you change the thermostat?
it could be a couple of things you could have a bad thermostat or a bad heater core
Your heater core is plugged and you need a thermostat.
Check into the temperature control valve--this is different than the thermostat.
flush out heater hoses
Low coolant? Wrong thermostat temperature range? Heater core plugged,restricted or airbound? Water pump not circulating coolant? Temperature control cable not adjusted properly?
I did a manual flush on the heater core with water from a hot water tank. I flushed a ton of crap out but did have to end up replacing the water pump.
The heater cor was replaced but it is still not getting warm
If a thermostat is not working properly, you cannot calibrate it. It must be replaced.
Thermostat probably needs to be replaced.