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Last night I was driving home and noticed that the heater wasn't blowing any hot air. I turned it up and nothing happened. I turned the fan-speed dial off, then turned it back on and hot air started to blow then.

When I got in my car this morning to go to work it again wasn't blowing hot air but was solved by turning the fan off then on again. Any ideas as to what might be causing this? It's nice currently that I can get it working but I don't want to discover some day in the dead of winter that it's suddenly quit completely!

The car is a Buick Century

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When the heater is not working, is it blowing cold air or not blowing at all? –  Gabriel Mongeon Nov 17 '11 at 19:49
It blows cold air just fine—it just never warms up. –  Vecta Nov 17 '11 at 20:40
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up vote 3 down vote accepted

If the fan is blowing, but no hot air is coming out that means that no hot water is making it into the heater core.

I can think of 3 reasons for this, each with a different solution.

First, and easiest to check: make sure that there's enough coolant in the car. If it's low, there may not be enough fluid to circulate through the core.

Second, the valve that opens to allow hot water into the core could be blocked (or the core itself could be blocked). You may be able to check this by undoing the intake and return lines from the core and seeing if you can get water flowing, perhaps by putting a hose on the intake. Be careful about applying too much water pressure, though - you don't want to blow up the core and end up with a very wet interior and a very expensive repair.

Finally, if you have an automatic climate control system, it could be a sensor that thinks there's too much heat going though the system, so is cutting off the flow of how water into the heater core. If it's an old mechanical system, the actuator may have come loose, so it's no longer operating the valve. If it's a sensor or other electrical gremlin, you'll probably need to take it to the dealer, but if it's a mechanical system you can probably trace the link & see if the valve is operating properly.

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Thanks for the tips—I'll look into them. I discovered today that if it isn't working that I can turn the temperature dial all the way to cold, then back to hot and it will kick in then. Thanks again! –  Vecta Nov 18 '11 at 13:41
That sounds like a problem with the valve. –  chris Nov 18 '11 at 17:02
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