Civic heater problem

Have a 1988 Civic with a heater that only blows cold air no matter how warm the engine is. Put in a new thermostat, flushed the heater core(flows nicely), the mixing valve opens and closes, and the belts are tight. When I pull off the heater outlet hose (plug engine opening) coolant barely flows out. Is there such a thing as a weak water pump? Or could it be something else? Any ideas are appreciated.

You lose any coolant at all? heater core maybe.

if the impeller on the water pump wasnt working properly youd be experiencing overheating. are you sure the lines going from the motor to the heater lines are clear?