1996 Chevy S-10 fix the heater

MAKE SURE THE RADIATOR IS FULL OF COOLANT.
THEN WITH THE ENGINE WARMED UP CHECK THE HEATER HOSES GOING INTO THE HEATER CORE AT THE FIREWALL. IF NIETHER ONE IS HOT, THEN REPLACE THE THERMOSTAT. IF INLET HOSE IS HOT AND THE OUTLET HOSE ISN'T THEN YOU NEED TO MAKE SURE THE HEATER CONTROL VALVE IS OPENING ALL THE WAY ALLOWING COOLANT TO FLOW THROUGH THE HEATER CORE. IF IT IS OPEN THEN YOU'LL NEED TO FLUSH THE HEATER CORE OR REPLACE IT.