High
E04 on Atag Q 25CR

Your boiler has detected an issue with the temperature of the water returning to the unit, suggesting the system is struggling to circulate water correctly or a sensor is misreading.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

°C return water temperature T2

Engineer required

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

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Related fault codes

E01View →E02View →E03View →

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