How much does it cost to fix Sime error code AL 56?

Typical repair cost for the Sime AL 56 fault is £120-450 including labour.

AL 56 High

Sime AL 56 Fault Code

Q: What does the Sime AL 56 fault code mean?

Your boiler has shut down because it detected a dangerous temperature difference between the water leaving the boiler and the water returning to it, suggesting it is overheating.

Also written as AL56 — same fault.

The Sime AL 56 fault code means: your boiler has shut down because it detected a dangerous temperature difference between the water leaving the boiler and the water returning to it, suggesting it is overheating.. It appears on 8 Sime models in our database.

Technical description: Lock for ΔT delivery/return over maximum limit — contact Technical Assistance

Typical repair cost £120-450 (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 56 fault code

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

Source

Sime AL 56 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 31 August 2026