203 High

Atag 203 Fault Code

The Atag 203 fault code means: your boiler is unable to read the temperature of your hot water cylinder, meaning it cannot heat your hot water correctly.. It appears on 18 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 £120-220 (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 31 August 2026