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Shuts down in 5 seconds? If so, it is supposed to. If the flame is not perfect. Read on..
The ignitor (glowbar) only glows for 5-7 seconds- just long enough to create combustion. Once the flame starts- the flame must keep itself going. So if at anytime the flame goes out- it stays out- there is nothing to restart it.
What most people don't realize is that the photocell is looking for a flame with perfect color, which means the heater is not emitting pollutants. If the flame runs too rich or too lean (polluting) the photocell shuts the unit down. No self re-start.
Start troubleshooting by setting the pump pressure. Pump pressure is directly related to fuel delivery. Poor fuel delivery equal poor flame equals shutdown.
Let's getdown to basics. You have already done the most basic, and time saving task- that being setting and monitoring the pump pressure. What youmust troubleshoot:
is the problem fuel related? or
is the problem electronics related?
To find outyou must eliminate all fuel related possibilities because there is not much wayto successfully troubleshoot the electronics without access to DESA'sdiagnostic tool- HA1170.Keep inmind that the ignitor only stays red for 5 seconds- just long enough to startthe flame- the flame must perpetuate itself. If at ANYTIME there is a momentaryflameout condition (or off-color flame condition) the heater will shut down.The photocell's job is to monitor the flame condition. If the photocell doesnot see a flame that it likes, then it will shut the heater down.If thisheater was in my shop and the customer described the problem, the first thingthat I would do would be
check the pump pressure- this is ALWAYS the first step.
shine a flash light into the fuel tank- inspect for water droplets in the tank
check for possibilities if a restricted fuel filter
check for possibilities if a restricted nozzle
with soapy water check for air leaks from the pump - all the way to the nozzle.
If all of these check out then remove the top cover. If the heater runs fine with the top removed- replace the nozzle. Desa recommended annual replacement.
The motor has an internal heat sensor. If the temp on the motor exceeds the safe level the sensor will shut the unit down. There is usually a pattern. The heater will run for an extended time, shut down, re-start, but the runtime is short. Let the unit cool and the pattern repeats itself. Feel the motor after shutdown. It should only be warm to touch. If hot, remove motor and bench test.. 2 possible causes- broken or grungy rotor or internal problems in the motor.
If it runs for awhile and then smokes and then shuts off, the problem is usually in the fuel system. If you have never serviced your unit, it may be time to do it. Most fuel tanks start sweating during the hotter times of the year. This moisture builds up and settles on the bottom of your tank. Your suction fuel line is real close to the bottom and the water in the fuel ends up spraying on the ignition plug or glow plug causing it to put out the flame and the units circuit board shuts down the unit because of a flame was not sensed. Check the fuel if it is not fresh, change it. Usually there is a drain in the bottom of the tank. Good luck.
The unit uses "flame rectification" (basically it is sensing a pulsing dc current) to sense the flame and is very sensitive to bad/poor ground and also to a dirty flame sensor. The gas ignition does not shut off the valve ...the board is not sensing the current thru the flame so its reading a "no Fire" fault and shutting down.
Clean the flame sensor with sandpaper till its brite and shiny and check all connections to make sure they are tight and very clean, especially the ground to the board and also to the furnace itself (sometimes we have to actually drive a ground rod near the furnace itself or use some other means to make sure that a proper gorund is achieved).
If still have a problem; I would try another board, the flame sensor is just a piece of solid stainless alloy wire so its really not necessary to change it unless the ceramic insulator is cracked.
Before you buy another board, I would suggest that you have a pro look at it.
the air pressure is not correct on either units.the photo cell DOES NOT look for light any more,it count the light flashes.if the flame is not in the right possition the heater will shut down....after the unit ignites the ignitor is no longer used to keep the unit working,just the fuel that is being fed to the flame ball.that's why the pressure is so inportant.......