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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