Webasto heater will not ignite when it is cold.when it is at operating temp it will ignite and run normal.

SOURCE: Cold Ait from heater ducts

u might want to check the blending doors that control ur ac and heater flow they tend to get stuck sometimes

SOURCE: 2004 grand prix heater will not blow hot air.

i have the same problem, i was just told to change the temp contol sensor which is only about $13.00 gonna change it friday!!

SOURCE: ford mondeo mk3, intermitent dumping of water from

You may have an air pocket in your system which some times happens.  One way to get rid of it is to take the upper hose off on the engine side,  fill your system with water until it runs out from your engine block, replace the hose, start your car turn you heater on and set to hi keep the radiator cap loose until the temp start to rise then close tight.  Once the air pocket had been remover you can drain some of the water from the radiator using the lower drain plug and add antifreeze.   

SOURCE: 1997 Bonneville SSE, when the heater is turned on, only cold air

you may have a failed blend air door motor/actuator. this part will regulate the amount of air from the heater core depending on the temp setting on your electronic climate control unit. if it has failed, it will be stuck at the temp that it was last set at when it quit working. it is also possible the heater core may be plugged up, but using the gm recommended dexcool coolant and flushing it out every 5 years, it should not be plugged up. you can pull the 2 heater hoses off the heater core on the passenger side of the engine compartment firewall and see if the heater core is the problem. caution-do not use a high pressure air hose to blow through the heater core as this could damage it and cause a leak!

SOURCE: My heater in my blazer does not heat. the engin

Hello. this is normallyt caused by a restricted heater core. under the hood on the passenger side of engine you will see two heater hoses going to the firewall. feel these hoses, they should both be hot to the touch. if one is cold and the other is hot, the heater core is plugged up. sometimes you can back flush the heater core and get the heat to work again.