Boiler leaking water from underneath the casing

Safety: Isolate electrical power before investigating leaks. Water inside the boiler can contact live parts.

• Turn off boiler: Switch off at the fused spur and close the cold water inlet (for combi models) if leak is significant.
• Remove front panel: If permitted by the user manual, remove the front cover and visually trace the source of the leak using a torch.
• Check common points: Inspect the Viessmann pump, automatic air vent, pressure relief valve, and visible joints for drips or staining.
• Contain leak: Place a tray or towels to protect flooring and prevent water reaching electrical components.
• Repair: Tighten accessible compression fittings gently. For leaking components (pump, AAV, heat exchanger), contact a technician to replace the affected part and refill/bleed the system.