My temperature says HI. but my temp is not warm

The error code is HL, not hi
This is telling you the high limit switch is tripping(safety feature)
Lack of flow, corroded heat exchanger, bad high limit switch, bad thermal regulator.....
Take these steps to try and get it narrowed down.
With heater off
Locate the high limit switch, unplug the two wires connected to it, put a jumper wire in between those two wires. Turn on the heater, if it fires you need to wait till it heats all the way up. If if heats up with no fault in the cycle then most likely it's a bad high limit switch, if it continues to trip then thermal regulator, it may need both parts.
If it doesn't fire at all then you will probably need a professional