In a boiler system, what must be installed for maintenance of the oil supply line?

For maintenance of the oil supply line in a boiler system, the installation of isolation valves and bypasses is essential. Isolation valves allow for specific sections of the pipeline to be shut off, which is crucial when performing maintenance or repairs. This ensures that the flow of oil can be controlled, minimizing the risk of spills and allowing work to be done safely without disrupting the entire system. Bypasses provide an alternative route for the oil to flow during maintenance, ensuring that the operation of the boiler can be maintained without significant downtime. This setup prioritizes both maintenance efficiency and safety in managing the oil supply.

The other options lack the comprehensive functionality needed for proper maintenance. Flow monitors are important for ensuring the system is operating as intended but do not facilitate maintenance activities directly. Pressure relief valves serve a different purpose, focused on preventing overpressure situations rather than assisting with maintenance. Heating elements are critical for the operation of the boiler, but again, they do not contribute to the maintenance of the oil supply line itself. Therefore, the combination of isolation valves and bypasses is the most effective choice for ensuring proper maintenance of the oil supply line in a boiler system.