Boiler leaking water from underneath, small puddle forming below the Defro unit.

Safety: Turn off power and close the heating flow/return and cold water isolation valves. Place a tray under the boiler to catch drips.

• Remove front cover: Inspect inside the Defro boiler with a torch to locate the highest visible point of moisture.
• Tighten fittings: Carefully tighten any slightly weeping compression or union joints. Do not overtighten plastic or cast components.
• Check air vent: If the automatic air vent cap is loose and leaking, gently tighten it, leaving it slightly open if required by the manual for venting.
• Seal replacement: If leaks are from O-rings or the plate heat exchanger, the affected seals or exchanger should be replaced using genuine Defro parts. This is typically a job for a qualified technician.
• Repressurize and test: After repairs, refill the system to the correct pressure, bleed air, and monitor for further leaks.