AL 17 High

Sime AL 17 Fault Code

Also written as AL17 — same fault.

The Sime AL 17 fault code means: your boiler has detected that its internal temperature sensors are giving conflicting readings, which stops it from running as a safety precaution.. It appears on 7 Sime 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: Fault regarding maximum deviation between the 2 NTC heating sensors — dual sensor models only
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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Sime models that show the AL 17 fault code

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

Source

Sime AL 17 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026