How much does it cost to fix Atag error code b25?

Typical repair cost for the Atag b25 fault is £120-£350 including labour.

b25 High

Atag b25 Fault Code

Q: What does the Atag b25 fault code mean?

Your boiler is heating up too quickly and has shut itself down to prevent damage, usually because water isn't flowing through the system correctly.

Also written as B25 — same fault.

The Atag b25 fault code means: your boiler is heating up too quickly and has shut itself down to prevent damage, usually because water isn't flowing through the system correctly.. It appears on 1 Atag model in our database.

Technical description: Boiler block: Temperature rise too fast

Typical repair cost £120-£350 (including labour)

DIY fix possible

Check that at least two or three radiator valves are fully openEnsure the boiler pressure gauge is between 1.0 and 1.5 barCheck if the pump is making a humming sound, suggesting it is stuck

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Atag models that show the b25 fault code

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

E Range Repair: £120-£350

Source

Atag b25 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