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▶ Check the ignition transformer function for misfiring in Menu 6, replace if required.
▶ Check the gas type.
▶ Check the gas supply pressure.
▶ Check operation of meter governor.
▶ Check the power supply.
▶ Check the electrodes; replace if required.
▶ Check the flue system; clean or repair if required.
▶ Check the gas/air ratio.
▶ Check the burner, replace if required.
▶ Check the air/gas ratio control valve; replace if required.