F.76 error, boiler shuts down, primary heat exchanger very hot

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Blocked primary heat exchanger, Pump failure, Severe air lock, Faulty thermal fuse or sensor on heat exchanger

Critical safety: Turn off power and gas. Allow the boiler to cool completely.

Checks (technician recommended):

Verify pump operation and system circulation.
Inspect the primary heat exchanger for scale or sludge blockage.
Check the thermal fuse or temperature sensor mounted on the heat exchanger; replace if open or damaged.
Flush or chemically clean the primary circuit if restricted.

This fault often requires professional cleaning or component replacement.

Professional Required 5/5

Primary Heat Exchanger

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