Boiler is excessively noisy during operation (rumbling, whistling, or fan roaring).

Safety first: Noise itself is not usually dangerous, but it can indicate developing faults. Do not remove covers while the boiler is running unless you are qualified.

Step-by-step checks:

• 1. Identify noise source: Carefully listen to determine if the noise comes from the fan, pump, or casing.
• 2. Tighten panels: With power off, tighten all accessible casing screws and ensure panels are properly seated.
• 3. Check pump mounting: Ensure the pump is firmly fixed and not transmitting vibration to pipework. Add pipe clips or anti-vibration mounts if needed.
• 4. Fan noise: Grinding or high-pitched fan noise usually indicates bearing wear and requires fan replacement by a technician.

When to stop: If noise is severe, new, or accompanied by error codes or smells, stop using the boiler and arrange service.