What does the Atag b18 fault code mean?

Your boiler has switched itself off because the water inside it has become too hot, likely due to a circulation problem.

How much does it cost to fix Atag error code b18?

Typical repair cost for the Atag b18 fault is £150-450 including labour.

Check that all radiator valves are fully open

Boiler block: Flow temperature > 95°C

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Each noise points to a different fault.

Sludge build-up — needs flushing, not bleeding.

Safety-critical — turn off, read this.