Heater blows cold air on 1997 Mercury Mountaineer

engine temp. is much higher than normal so i suspectd bad water pump but has no unusual noise, top radiator hose seems to have pressure. no leaks, fluid levels normal. appreciate any ideas. thx

Asked by for the 1997 Mercury Mountaineer
poss stuck closed thermostat because you say u are not losing coolant
appreciate your help...i had thought they failed in open only. will try repcl and let you know. thx again, mo