How much does it cost to fix Atag error code 78?

Typical repair cost for the Atag 78 fault is £90-180 including labour.

78 High

Atag 78 Fault Code

Q: What does the Atag 78 fault code mean?

Your boiler has detected that the water pressure is either too low or too high to operate safely, or the sensor that monitors this pressure has lost its connection.

The Atag 78 fault code means: your boiler has detected that the water pressure is either too low or too high to operate safely, or the sensor that monitors this pressure has lost its connection.. It appears on 4 Atag models in our database.

Technical description: Water pressure outside of range or not connected

Typical repair cost £90-180 (including labour)

DIY fix possible

Check the pressure gauge on the front of the boiler or via the display menu.If the pressure is below 1.0 bar, use the filling loop valves to top it up to roughly 1.5 bar.If the pressure is too high (above 3.0 bar), bleed a radiator to release some water and lower the pressure.Restart the boiler to see if the code clears.

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Atag models that show the 78 fault code

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

Source

Atag 78 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