heater is putting out very little heat on high position or any position on 1996 Audi A6 Quattro

drove into town heater worked fine, on the way back home it put out very little warm air, all the heater controls work fine but very little heat

Asked by for the 1996 Audi A6 Quattro
ck coolant level you may have a leak you haven't noticed
1 more answer
check your coolant level if ok replace thermostat its the cheapest place to start