I have a afg beckett gun. It is about 10 years old. I tuned it up about 3 months ago. New filter, electrodes,nozzles & set the adjustments of the electrodes. 2 weeks went by then the relay tripped. Reset then 8 days till next tripped relay. Then every 5 to 7 days over & over for 2 months. I changed the transformer,oil pump blew back the supply line but not the return line. Put a new relay on. New cad cell. Cleaned burner & flu. Made it 8 days tripped again. My tank is below ground no water. Does anyone have any ideas. Thank you. I've been tunning up burners for twenty years plus at least a total of 2 to 3 hundred total over the years. Nothing like this ever happened?