The most common oil boiler faults | and what they actually mean
Lockout on start-up: usually a worn nozzle, dirty photocell or a fuel supply issue. Rumbling or delayed ignition: nozzle sizing, air setting or an electrode gap out of spec. Sooting inside the boiler casing: combustion running rich, often nozzle, air damper or a fuel pump losing pressure. Kettling and expansion noise: heat exchanger fouled, poor circulation or system water quality. Pressure won't hold: expansion vessel gone flat, PRV weeping, hidden leak on system pipework. Boiler fires then stops on flame failure: photocell, electrodes, transformer or fuel supply. We work through them in diagnostic order, verify with instruments and fix the cause, not the symptom.
