Sime AL 62 Fault Code: Causes, Fixes & Repair Costs
What does the Sime AL 62 fault code mean?
AL 62 on a Sime boiler means the appliance is demanding its automatic self-calibrating procedure be carried out. Sime's combustion-control models continuously manage their own gas/air ratio against a calibrated baseline; certain events — replacing the gas valve, electrode, burner, fan or control board, parameter resets, or the controller detecting it has lost a valid calibration — require the full self-calibration to be rerun before normal operation continues. AL 62 is the boiler saying that baseline is missing or invalid. The remedy is exactly what the manual says: perform the self-calibrating procedure, which an engineer runs from the panel with hot water drawn off to dissipate heat, followed by a flue-gas analysis.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Component replaced without recalibration Common
Sime's manual is explicit: replacing the gas valve, ignition/detection electrode, burner or fan requires the full self-calibration afterwards. If that step was skipped, AL 62 appears. The same applies after board replacement and parameter set-up.
- Calibration data lost or invalidated Sometimes
Parameter resets or a board issue can invalidate the stored calibration, prompting the boiler to demand a fresh one even without recent parts changes.
- Underlying combustion problem preventing calibration Sometimes
If calibration was attempted and could not complete, associated combustion faults (see AL 90/92/93) may accompany AL 62 — pointing at the electrode, flue or gas supply rather than the procedure itself.
How to fix it
- Think back to recent work DIY safe
If the boiler has just been serviced or had parts fitted, contact that engineer — completing the self-calibration is part of the job Sime's manual requires after such work.
- Reset once with the OK/RESET button DIY safe
Hold the OK RESET button for more than 3 seconds. Sime boilers allow a limited number of consecutive resets (six) before locking out on AL 28, so if the code returns after one or two attempts, stop and book an engineer rather than using them all up.
- Have a Gas Safe registered engineer carry out Sime's documented remedy Gas Safe engineer
The engineer starts the automatic self-calibrating procedure from the panel (holding OK and + as per the manual), draws hot water to dissipate heat while it runs — up to around 15 minutes — and completes a flue-gas analysis afterwards to confirm combustion. That clears AL 62; if calibration will not complete, they diagnose the accompanying combustion codes.
Parts you may need
- Ignition/detection electrode · from £35
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£250, depending on the underlying cause.
Frequently asked questions
What does AL 62 mean on my Sime boiler?
The boiler requires its automatic self-calibrating procedure to be run — its combustion baseline is missing or invalid, most often because a combustion component or the board was replaced without the mandatory recalibration afterwards. An engineer runs the procedure and verifies combustion; there may be nothing 'broken' at all.
Why do Sime boilers need calibrating?
These models actively manage their own gas/air ratio using feedback from the flame, tuned against a stored baseline set during commissioning. Change a combustion component and the baseline no longer matches the hardware — so Sime requires the self-calibration to be rerun, protecting efficiency and combustion safety.
How long does it take and what does it cost?
The procedure itself takes up to about 15 minutes plus a flue-gas check — a short visit, typically at the lower end of £80–£250 unless an underlying combustion fault emerges during calibration.