Boiler troubleshooting starts with checking the electrical and fuel connections, which are needed to power other components. Combustion components and ventilation equipment should also be checked.
Newer boilers require an electrical connection to power sensors and interfaces. If the boiler has a digital display that won't turn on, the problem is likely electrical. The gas line or oil tank should then be checked to ensure the unit is receiving fuel. If the pilot light won't stay lit, the problem may be with the gas line.
Boilers also need a source of combustion to properly fire. Electrical ignition systems, which are common on newer units, often make a clicking sound when they fire; listening for this sound when the unit operates correctly can help users know what to listen for. Units that fire but quickly go out may be affected by a problem with the gas line or oil nozzle, but it's also important to make sure the combustion area is free of debris and buildup.
Boilers require proper ventilation to function properly, and boilers that start and stop intermittently may have a problem with venting away carbon dioxide and other chemicals. Newer units may also switch of if inefficient combustion is detected since this can cause the formation of carbon dioxide.