The likely reason you can't find a leak is because the coolant is escaping when the system is cold and dripping right into your cabin. To confirm this, check the passenger side floor for moisture. Your heater isn't working. Another glaring sign of a bad heater core is a simple lack of heat.
Similarly, why is my central heat not working?
If your boiler seems to be working and your hot water supply is still functioning, but your central heating is not working, then the problem is either down to the settings on your boiler and central heating system or because a component of the boiler – almost certainly the motorised diverter valve – is broken.
Why is my heat blowing out cold air in my home?
Thermostat: A Furnace Blowing Cold Air Could be Due to Your Thermostat. Again using Occam's Razor, we can assume that the next likely culprit for your heater blowing cold air is your thermostat. This can cause your heater to blow cold air due to improper temperature inputs from the thermostat.
Why does my heat keep turning on and off?
This is most common cause of short cycling. A dirty air filter restricts air from getting into your furnace. Your furnace's heat exchanger needs that air blowing over it or it overheats, causing the furnace to shut down. Change (or wash, if you have a washable type) your air filter if it's dirty.