Engine is running hot but heater is blowing cold

Shut the engine off. When it cools down (20-30min later)check your coolant levels. If your low/out of coolant you will not have heat.engine runs hot..If your Thermostat is sticking you won’t have heat and engine runs hot.. also maybe water pump.Are you leaking any coolant.?

check coolant level in reserve tank, if full, could be a bad thermostat OR a plugged heater core.