Feel the temperature of the heater pipes in the engine bay, where they pass through the front bulkhead.
If they are both hot then the fault is most likely the air regulator flap stuck.
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It could be a faulty wiper Motor or short circuit in wiring related to wipers.
Could be a bad thermostat or heater core
Could be a Faulty relay.
it could be a couple of things you could have a bad thermostat or a bad heater core
Your car could be low on antifreeze or your heater core could be clogged. With my car, it was Heater matrix clogged with radiator sealant. The workshop cleaned it and it's start working fine!
there is a short somewhere in dash or heater, you need to fix that to stop fuses blowing
A common cause is the thermostat being stuck in an open position.
Acabin air filter (if fitted) could be blocked. The heater matrix or pipes to it could be furred up. A cooling system flushing treatment might do the trick. Failing that a strip out and cleaning the crud from between the matrix fins might be the answer. If all else fails a new matrix might be required.
It could be a thermocoupler, happened to my furnace in middle of night a few years ago.
could be head gasket problem. does your heater work? might need heater core , clogged up. do compression test. or bypass heater core and see if that works.
Thermostat stuck open, clogged heater core, heater flow valve not functioning, or low of coolant.
It could be the heater valve which is located under the hood to the passenger side down below the radiator and fan units.