Heater problems
 

I have a problem with my heater, and I want to fix this before winter hits me. My heater won't heat. Now, it's not a complete lack of heat. It will start out heating about 15-30 seconds worth of heat, but then, the heated air starts to turn cool. The only thing I can think of is that maybe the core is clogged up and only a small flow of water is going through...just enough to accumulate some heated air for the 15-30 seconds that it works.

Is this a possibility?

Feel the hose going in the core if its getting and staying hot. Also feel the hose comming out. Not hot coming out, clogged.

You can flush it with a garden hose. Unhook both hoses. This will also get out excess air.

Air pockets will cause the same problem you describe also. Because the core sits high.