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BBQ won't hold light

Hi there We purchased a bbq second hand off trade me (Gas Craft Serrano, 6 burner), but listing said it was never used. Just assembled and stored for a year. We turned it on and the burners just won't stay lit. They'll ignite for 10-30 seconds and then go out. We've tried cleaning and replacing the regulator hose but still no luck. Can you help? Erin