AL 02 High

Sime AL 02 Fault Code

Also written as AL02 — same fault.

The Sime AL 02 fault code means: your boiler has stopped working because the water pressure inside the heating system has dropped below the minimum level required to operate safely.. It appears on 22 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: Low water pressure in the system
Typical repair cost £80-150 (including labour)

DIY fix possible

Locate the external filling loop, which is a silver braided hose connecting two pipes under the boiler.Open the small valve or tap on the loop to allow water into the system, watching the pressure gauge on the front of the boiler.Close the valve firmly once the needle on the gauge reaches between 1 and 1.5 bar, then check the boiler for the fault code to clear.

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Sime models that show the AL 02 fault code

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

Source

Sime AL 02 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