Boiler runs but makes loud humming or grinding noises from inside the casing.

Safety first: Isolate power before touching the pump or internal components. Beware of hot surfaces.

• Identify noise source: Remove the front panel and carefully listen to locate whether the noise comes from the pump, contactors, or vibrating pipes.
• Bleed pump: If the pump has a bleed screw, release trapped air until water flows steadily, then retighten.
• Tighten fixings: Check that the pump, brackets, and any internal components are securely mounted. Tighten loose screws.
• Support pipework: Add or adjust pipe clips to prevent pipes from vibrating against the casing or walls.
• Replace noisy pump: If the pump bearings are worn (grinding noise) or the pump overheats, replace the pump assembly.