Sime AL 82 Fault Code: Causes, Fixes & Repair Costs
What does the Sime AL 82 fault code mean?
AL 82 on a Sime boiler is the block raised after numerous combustion-control failures — the boiler has tolerated repeated individual combustion deviations (the kind logged transiently as AL 83) and has now concluded the problem is persistent, so it locks out. Sime's documented checklist for this family covers the ignition/detection electrode, the flue inlet and outlet, the air diaphragm, and the gas calibration and supply. Think of AL 82 as the combustion controller's escalation: not one bad moment, but a pattern it will no longer run with. That pattern usually traces to a deteriorating electrode giving poor flame feedback, a partially blocked flue, or a gas/air relationship that has drifted from calibration.
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
- Deteriorated ignition/detection electrode Common
The electrode is the combustion controller's eyes: worn, cracked or badly gapped, it feeds back a noisy flame signal that repeatedly fails checks until the boiler escalates to AL 82. It is the first item on Sime's list and the most common finding.
- Partial flue restriction Common
A partially obstructed inlet or outlet degrades combustion continuously rather than catastrophically — exactly the pattern of repeated small failures this code represents.
- Gas calibration or supply drift Sometimes
Supply pressure sagging or the calibrated gas/air baseline no longer matching reality (see AL 62) leaves every burn slightly wrong. Recalibration after rectifying the cause is part of the fix.
- Air diaphragm degradation Sometimes
Sime's checklist includes the air diaphragm — a degraded diaphragm shifts the air side of the mixture and undermines every combustion cycle.
How to fix it
- Check the flue terminal visually DIY safe
An external look for obstruction is the only combustion check that is homeowner-safe. Everything else on this code is sealed-case work.
- Reset once with the OK/RESET button DIY safe
Hold the OK RESET button for more than 3 seconds. Sime allows a maximum of six consecutive resets before locking out on AL 28, so if the code returns after one or two attempts, stop and book an engineer.
- Have a Gas Safe registered engineer work through the combustion-control checks Gas Safe engineer
Sime's documented checklist for the combustion-control faults covers the ignition/detection electrode (condition, position and earthing), the flue inlet and outlet for blockage, the air diaphragm, the gas calibration and supply pressure, and bleeding air from the gas circuit where relevant. After rectification the engineer reruns the automatic self-calibrating procedure and confirms combustion with a flue-gas analysis.
Parts you may need
- Ignition/detection electrode · from £35
- Air diaphragm · from £15
- Gas valve (SGV) · from £150
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 £120–£380, depending on the underlying cause.
Frequently asked questions
What does AL 82 mean on my Sime boiler?
The combustion-control system has recorded repeated combustion failures and locked the boiler out — a pattern, not a one-off. Sime's checklist runs electrode, flue, air diaphragm and gas calibration; the electrode is the most frequent culprit, and a recalibration follows the repair.
I saw AL 83 a few times before AL 82 — is that connected?
Yes, directly. AL 83 is the transient irregular-combustion warning; enough of them and the boiler escalates to the AL 82 block. Mention the history to your engineer — it confirms the persistent pattern the code implies.
Will a service prevent AL 82?
Largely, yes. Electrode condition, flue integrity and combustion readings are exactly what an annual service on a combustion-control boiler covers — this code is often the eventual price of skipped servicing.