My heater wont stay lit. it shuts down and has a "no ignition" code i cleaned the photo eye, and even shine a light in it after it lights and it seems to be working. if i shine a light in it after it lights then it shuts down and says its out of fuel.

clean/replace the flame sensor. Your heater doesn't recognize that it has lit and continues to try and light the gas. when the sensor doesn't tell the 'brain' it lit? it shuts down the gas for safety reasons.

Some heaters have to be "warmed up" by holding the button down for approx. 30 seconds after it lights. These are ones with whats called a "thermocouple". The thermocouple has to remain a certain temp. or the unit will shut off. If the thermocouple goes bad, it can be replaced

Might work. Might not. Depending if the eye can sense light and dark from that position. If area is shaded, then the sensor might think it's dark earlier in evening. If the area is dark, then sensor will not do as well, or might stay ON full time.
If the outdoor light shines on nearby surface, the reflected light might cause photo eye to blink on-off throughout night.. or not function as expected.
You can add separate photo eye to any light, and choose location for photo eye.
http://waterheatertimer.org/How-to-install-and-troubleshoot-photo-eye.html
Add a comment and say what you discover, or for followup wiring question.

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Hello, if the burners light but do not stay on for more than 10 seconds, I would clean the flame sensor. The flame sensor is a metal rod that is on the opposite side of the Igniter, sometimes it gets coated by oxidation and does not sense the burner flame and shuts the Furnace down. To clean to kill power to tje furnace, remove flame sensor and clean with a steel wool, then reinstall and start Furnce back up. If this does not work then most likely the Igniter is too weak to ignite the gas and will have ro be replaced.

The test- per DESA

I would first check the gas pressure to your furnace. Then make sure that burners are clean and watch flames when burner first ignites. I have seen burners that were dirty cause delayed ignition that would create a suction when they came on and extingush pilot and burners.
The next thing I would do is change gas valve. Thank you

You can try repositioning the photo electric eye by slightly bending the holder up or down. I would look at it and make sure there is nothing on the lens and clean with windex dampened terry cloth rag.This is not recommended but you can by-pass the photo electric eye and if it stays running you have found the culprit. You are not clear as to if it even lights, these suggestions are good only if it ignites. Hope this helps you out.

The photo eye shuts the unit down if the burner does not burn correctly on startup, ie.if the eye does not see light prior to tiiming out. I would say since it is shutting down, it is working OK. While you say there is plenty of fuel, you do not know if there is the correct ratio of air to fuel. The most common problem on these heaters is the mix. I have a tip at http://www.fixya.com/support/r4124129-yearly_maintenance_reddy_heaters which explains exactly what you need to do to correct this and where to get the parts to do it. Let me know if you need anymore help.

hardrocko

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sounds like a clogged orifice or obstruction in the the fuel line

Try cleaning your filter if dirty there will not be enough flow to llet heater fire. If filters clean you can try jumping the pressure switch.