This is posted in the wrong section. If you are unsure where to post, most of the sections are labeled in the main directory or in a sticky at the top inside of that section.
Thread moved to MKIII General.
To answer your questions, the coolant level sensor is inside the coolant reservoir. If that is below a certain level the light on the dash will light intermittently and if empty the light will remain on.
Lack of heat may be due to a common issue with the heater control valve (HCV). Specifically, the controlling VSV dies and the flow stays shut routing coolant away from the heater core instead of through it. See the MKIII FAQ section for more info on diagnosing it and how to bypass it for the time being.
As you have both a low coolant level AND lack of heat it is plenty possible that you do have a coolant leak and a significant amount of air in the system which you simply aren't seeing. Keep a close eye on the coolant reservoir and its level, to level of coolant in the radiator (when it's COLD), and if the heater control valve is functional then you may want to have the cooling system flushed and pressure tested.
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