If your unit is more than a couple of years old you probably need to change the filter in the back and set the pump pressure. A good indication that you need to do this is if your unit turns on, starts to heat, and almost immediately stops and blows smoke out of the end. The air/fuel mixture is not correct, probably due to a partially clogged filter. These heaters use the air pressure to determine the amount of fuel to pump. Obviously if the pressure is not correct, too little or too much fuel will be pumped. Either situation causes the unit to shut down and smoke.
Both the filters and the gauges to set the pressure can be found at www.reddyparts.com
along with a good explanation as to why you need the gauges. If you want your unit to run properly, and efficiently, I recommend purchasing the gauges. They make setting the units easy as well as possible.
The pressure is set by bleed air pressure and must be exactly 3.5 psig. The gauge is the only accurate way to do it. The filters clog and change the pressure. When the difference is enough the unit will not run.
Now with that said there are several other things which you should check yearly. Check the fuel tank for water. Remove any you find by draining the unit. Remove the cover on the right side, as you look at the unit from the front, and remove the circuit board. Check for cracked connections. These things vibrate alot. If you find any broken solder connections resolder them and reattach the board. Until I completely resoldered my board I kept having problems.
That should take care of the unit and get you back to making heat.
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