Boiler leaking water from underneath the casing

Safety first: Isolate electrical power. If the leak is significant, close the system isolation valves and, if safe, the cold water supply to the boiler. Beware of hot water and surfaces.

• Identify source (visual): Remove the front panel if allowed and look for the highest visible point of moisture. Check around the ACV safety relief valve discharge pipe, pump unions, and automatic air vent.
• Check pressure relief discharge: If water is dripping from the relief valve discharge pipe outside, the valve may be passing due to overpressure or debris.
• Do not ignore corrosion: If the primary heat exchanger or tank-in-tank cylinder shell is visibly corroded and leaking, the unit will likely need major repair or replacement.
• Professional repair: A technician should replace faulty valves, seals, or the heat exchanger, and check expansion vessel charge to prevent recurrence.