Navien Gas Orifice 20058413A

The gas orifice is a Navien component that meters the flow of natural gas into the burner on NCB300 and NCB500 combi boilers. It is sized for natural gas (NG) operation and forms part of the gas train, setting the input rate the appliance can deliver. Correct orifice fitment is essential to combustion performance and safe operation.

• Gas rate or heat input measured at the meter falls outside the values stated for the appliance
• Combustion readings (CO, CO2 or O2) drift outside the specified range and cannot be corrected by adjustment
• Unstable or weak flame at the burner, or the boiler failing to reach its rated output
• Sooting, discolouration or debris visible at the orifice or burner area
• The orifice is damaged, distorted or has been fitted with the wrong size for the gas type

• Confirm the boiler model and serial number against the fitment list above, as orifice sizing differs between output variants
• Verify the appliance is set up for natural gas (NG) and not LPG, as the two require different orifices
• Compare the existing orifice against the new part before fitting to confirm the size and gas type match
• Work on the gas train must be carried out by a Gas Safe registered engineer, with the gas supply isolated and combustion re-checked after fitting