04 Saturn vie 3.5 heater not getting warn
 

Get the engine up to operating temp and grab the inlet and outlet hoses for the heater core. Are both hot.

Also, are you sure there was heat output before your work?

May just need to burp the air out of the cooling system.

Derf beat me to it. I was going to inquire if the heat worked before the water pump replacement. Is the system full of coolant and did you flush the heater core before refilling it? If not, do a flush and reverse flush on the heater core and see what happens. It may be full of crud.

yes everything worked fine befor I done the timing belt replacement

Please answer my questions above as part of troubleshooting.

Thanks

Mine does the same thing intermittantly. when really cold the heat will not work. The engine light came on with a P0116 Code so I replaced the coolant sensor. This morning while it was cold out 19 degrees, and the car was running for 20 min - still no heat.
I checked both lines coming out of the heater core and both were hot.
I just got the car (a 2001 L300) and the past owner said he changed the thermostat.
Even after replacing the coolant temp sensor the engine light came on again this morning with the same code.
I'm not really trusting what a past owner said, but would anyone else think it could be something besides the thermostat? Thanks in advance!!

Thanks! I will start a new thread. The heater panel I have is the two manual knobs.