Your boiler is struggling to transfer heat to your hot water because a key internal component is likely blocked or damaged.

Water to Water Heat Exchanger Giannoni, Ref. PVW 14 E

What causes this fault?

This fault occurs when the boiler's internal sensors detect that heat isn't being transferred effectively to your taps, usually due to a buildup of limescale or heating sludge inside the secondary heat exchanger. The most common reason is 'sludging' from the main heating circuit, which creates a physical blockage that prevents the cold water from heating up properly. In some cases, a failing diverter valve may also be preventing the hot water from flowing into the correct part of the system.