203 High

Atag 203 Fault Code

The Atag 203 fault code means: your boiler has lost connection with the sensor that monitors the temperature in your hot water tank, meaning it cannot heat your water correctly.. It appears on 2 Atag models in our database.

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: Tank Probe Damaged (Solo)
Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Atag models that show the 203 fault code

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

Source

Atag 203 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 7 July 2026