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If the ohmmeter reads zero or open, the cell should be checked for dirt on the face or shorted leads. If the face of the photocell is dirty, clean with soft cloth and replace. Check for the resistance change in the photocell from no flame to flame. If the cell still reads zero or open check the wiring from one end to the other for opens and across the leads for shorts. If no problem is found replace the cell and check once again for the resistance change. 5. If the photocell and primary safety