Boiler displays error code A02, indicating an overheat condition; the boiler becomes very hot and then shuts down.

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

Pump failure, Air in system, Blocked primary heat exchanger, Closed valves on flow/return

Safety first: Allow the boiler to cool fully. Do not remove caps or bleed valves while hot.

Check system pressure: Top up to 1.0–1.5 bar cold if low.
Bleed radiators and towel rails: Remove trapped air and re-pressurize.
Check isolation valves: Ensure flow and return valves under the boiler are fully open.
Engineer checks:
- Verify pump operation and free rotation.
- Inspect the primary heat exchanger for blockage.
- Check bypass and system design.

Repeated A02 faults indicate a circulation or scaling issue that needs professional attention.

Hard 4/5

Primary Heat Exchanger

Check Price on Amazon

We may earn a commission from links on this page.