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

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

b18 High

Atag b18 Fault Code

Q: 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.

Also written as B18 — same fault.

The Atag b18 fault code means: your boiler has switched itself off because the water inside it has become too hot, likely due to a circulation problem.. It appears on 1 Atag model in our database.

Technical description: Boiler block: Flow temperature > 95°C

Typical repair cost £150-450 (including labour)

DIY fix possible

Check that all radiator valves are fully openCheck the boiler pressure gauge and top up to 1.5 bar if lowCheck for any blocked or frozen external condensate pipesPress the Reset button once the boiler has cooled down

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Atag models that show the b18 fault code

Click a model for the full fault code list and model-specific repair notes.

E Range Repair: £150-450

Source

Atag b18 fault code information on this page is sourced and cross-checked against the official Atag service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026