Heater runs too hot

Have you checked all your fuses ? Then you might want to verify that you don't have a leak of refrigerant from your vehicle A/C system.

Either your heater core is plugged or the blend door under the dash is not moving from cold to hot. Do you hear any noise from under the dash when you move the dial from coldest to hottest? If not then likely the blend door is stuck in the cold position.

Stuck ignition relay possible. With hot battery, turn key off and then feel each relay. If you find a hot one, change it.

Sounds like an air lock!
To Check....
With engine cold set heater to hot position.
ID return pipe from heater under the hood. Remove the return pipe at one end to check if coolant is there ( it should run from heater pipe) if no coolant you have an air lock.
To remove air lock top up coolant header when engine is cold. Leave heater in cold position replace pipe and start engine. Allow it to come to working temp then set heater to hottest position. Allow a few seconds and check if the pipe you first removed is hot. If no then ease the securing clip and carefully allow air to escape while engine is running... place a cloth over this area to prevent hot coolant spraying out. When coolant appears re-tighten pipe.
"PLEASE BE VERY CAREFUL DOING THIS AS COOLANT WILL BE EXTREMELY HOT".
If you're not confident enough to do this ask a qualified mechanic to do it for you.
Again please be careful.

Check your blower motor resister,it's next to the blower.

If it seems to blow even hotter air when the A/C is on then yes you have a leaking A/C system. It will still activate because it isn't empty yet. Another possibility is the temp door actuator isn't closing to the cold position. When you turn the fan off or to low, adjust the temp from full hot to full cold (just with key in run position, not with engine running). Look up at the heater control box on the drivers side just above the gas pedal, and you should see a white triangular plastic box. You should hear the actuator move or even see the rod in center of box turning. If not the actuator is faulty.

under the alternator there is a control valve located in line from the water pump to the heater core, your control switch operates this valve via air. have someone or you can do it yourself turn switch to hot,LOL already there,ok locate this valve and notice the position of the rod on valve. now turn control switch to cold position, recheck position of rod again, did it move? pull air line off valve,or follow air line up a little bit and you will find a coupler, you can disconnect it here. while engine is running put finger over hose and check for suction in cold and hot position. Should only **** in hot position. if ok your inline valve is bad. cheap fix

Most cars and trucks are set for the A/C to run in defrost. Even if you have the temp at hot. The air will pass through the evaporator core first witch draws moisture out of the air. That is why you see water dripping out of a car with the air on and sitting at one place.

The dry air makes the defroster work faster. It is a safety feature.

There is small cable that runs from the back of the temp control switch on the console that goes through the firewall and loops around a valve on the heater hose that is used to control the amount of hot coolant that goes into your heater coil. This cable hooks on the back of the temp control switch also. Bad news, that's probably where it came off and you'll have to pull the control unit out of the dash to get to it.

Check the water contol valve operation ( under hood connected to heater hoses), do you have a full load of coolant?, also air mix door under dash, is the temp of the coolant hot?.Check them all out, you'll find it