How much does it cost to fix Atag error code FILL (flashing)?

Cost varies. Contact a Gas Safe registered engineer for a quote.

FILL (flashing) High

Atag FILL (flashing) Fault Code

Q: What does the Atag FILL (flashing) fault code mean?

Your boiler has detected that the water pressure inside your heating system is too low, meaning it needs to be topped up with more water to work correctly.

Q: Can I fix Atag fault code FILL (flashing) myself?

Locate the external filling loop, which is usually a flexible silver braided hose connecting two pipes near the boiler.

Also written as FILLFLASHING — same fault.

The Atag FILL (flashing) fault code means: your boiler has detected that the water pressure inside your heating system is too low, meaning it needs to be topped up with more water to work correctly.. It appears on 7 Atag models in our database.

Technical description: Water pressure is to low (<1,0 bar), flashing FILL will be altered with indication of water pressure, boiler power of 50% is possible. The installation needs to be topped up.

DIY fix possible

Locate the external filling loop, which is usually a flexible silver braided hose connecting two pipes near the boiler.Open the valves at both ends of the filling loop to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves firmly and ensure the filling loop is disconnected if required by your specific installation.

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Atag models that show the FILL (flashing) fault code

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

Source

Atag FILL (flashing) 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