No heat

[McCohens at aol.com]

My 5000 TQ has very little warm air.  I disconnected the temp system and have 
the flaps set to defrost only, coolant valve fully open.  The A/C is unhooked 
also.  I blew the heater core out today, thought it might be clogged but not 
so.  The hoses to and from the heater core are warm.  If the fan is off, once 
turned on it puts out warm air for about 30 seconds, then the air is barely 
warm.
Could a bad water pump cause this?  I was wondering if the impellers are 
really worn maybe they don't move much water.  Also thinking about hot wiring the 
turbo water pump, which terminal would be hot to make the pump work in the 
correct direction.  Any ideas appreciated.