Vokera AL52 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera AL52 fault code mean?
AL52 is a 'final' lockout alarm on Vokera boilers, meaning the boiler has detected an internal fault it cannot assign to a specific external cause and has shut itself down as a precaution. The boiler will not restart until it has been manually reset. Because the fault is classed as internal, the boiler's control system has flagged an electronic or PCB-level issue rather than something straightforward like low pressure or a frozen condensate pipe. A single reset is always worth attempting, but if AL52 returns, it is a strong signal that a Gas Safe engineer needs to investigate the electronics or internal wiring.
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
- Transient electronic glitch or power interruption Common
A brief power cut, voltage spike, or momentary supply fluctuation can cause the boiler's control board to log an internal fault and lock out. In these cases the boiler is otherwise fine, and a single reset will clear the code permanently. This is the most benign explanation and should be ruled out first.
- PCB fault or failure Common
The printed circuit board (PCB) acts as the boiler's control centre. Corrosion, a blown component, moisture ingress, or age-related degradation can cause the PCB to raise an internal alarm. If AL52 reappears after resetting, PCB failure is the most likely culprit. A Gas Safe engineer will inspect for burn marks, damaged tracks, and failed components before deciding whether the board can be repaired or needs replacing.
- Internal wiring or connector fault Sometimes
Loose terminals, chafed wiring, or a corroded connector between the PCB and another internal component can trigger a spurious internal fault code. This is particularly common on older boilers where vibration over time works connections loose. An engineer will check harness integrity and reseat or replace any suspect connectors.
- Failed internal electronic component Rare
Other electronic components such as the ignition module circuitry or an onboard sensor interface can degrade and cause the PCB to report an internal error even when the broader boiler components appear intact. This is harder to diagnose without specialist equipment and generally requires a Gas Safe engineer with manufacturer-level diagnostic tools.
How to fix it
- Reset the boiler once DIY safe
On most Vokera models, press and hold the reset button (marked 'R') for around 3 to 5 seconds until the fault code stops flashing, then release and allow the boiler to restart. On dial-operated models, turn the selector to the reset or off/reset position and hold briefly. Watch the boiler for 10 to 15 minutes to confirm it runs a full heating or hot water cycle without AL52 returning.
- Check the electrical supply DIY safe
Ensure the boiler has not lost power due to a tripped circuit breaker or blown fuse at the consumer unit. If a circuit has tripped, reset it once. Also check that the boiler's fused spur switch is on. If the electrics trip again immediately, stop and call an electrician or Gas Safe engineer.
- If AL52 returns after resetting, stop resetting and call a Gas Safe engineer Gas Safe engineer
Repeatedly resetting a boiler with a genuine internal fault risks masking a developing problem or causing further damage. If the code comes back after one or two resets, the underlying cause needs professional diagnosis. A Gas Safe engineer will use diagnostic equipment to check the PCB, inspect internal wiring and connectors, and identify which component is causing the fault before carrying out any repair.
- Have the PCB inspected and repaired or replaced if necessary Gas Safe engineer
If the engineer identifies PCB failure as the root cause, they will assess whether the board can be repaired (for example, by replacing a single component) or whether a full replacement board is required. Only a Gas Safe registered engineer should carry out this work, as incorrect handling of the PCB or associated wiring can cause further damage or create a safety hazard.
- Request a post-repair operational check Gas Safe engineer
After any internal repair, ask the engineer to run the boiler through a full heating and hot water cycle and confirm that AL52 does not recur. This is standard practice and ensures the root cause has been fully resolved rather than temporarily suppressed.
Parts you may need
- Vokera PCB (control board) · from £180
- PCB wiring harness · from £45
- Ignition module / ignition lead assembly · from £35
- Internal connector set · from £20
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 £150–£400, depending on the underlying cause.
Frequently asked questions
Can I fix Vokera AL52 myself?
The only step a homeowner should take is a single boiler reset. If AL52 clears and does not return, no further action is needed. If it reappears, the fault is likely electronic and requires a Gas Safe registered engineer to diagnose and repair safely. Attempting to access the PCB or internal wiring yourself could void any warranty, cause further damage, or create a safety hazard.
How much does it cost to repair a Vokera AL52 fault in the UK?
For most people, the repair falls between £150 and £400, covering the engineer's call-out or diagnostic fee (typically £60 to £100) plus labour and any parts. If the PCB needs a full replacement rather than a component-level repair, costs can rise to £450 to £700 depending on the exact model and your location — London and the South East typically sit at the top of that range. It is worth checking whether your boiler is still within any manufacturer or installer warranty, as PCB replacements are sometimes covered if the boiler has been serviced annually.
Why does AL52 keep coming back after I reset it?
A recurring AL52 almost always means there is an underlying electrical or electronic fault that a reset cannot fix. Common culprits include a deteriorating PCB, a loose or corroded wiring connector, or a failing internal component. Each time you reset without addressing the root cause, the boiler will reach the same fault condition and lock out again. Book a Gas Safe engineer to carry out a proper diagnosis rather than continuing to reset.
Is AL52 dangerous?
AL52 itself is a control-system lockout rather than a direct gas or combustion safety alarm, so it is not immediately dangerous in the way that a carbon monoxide warning would be. However, because it signals an unspecified internal fault, you should not attempt to bypass the lockout or reset the boiler repeatedly. Leave the boiler off and arrange an engineer visit promptly, especially if the fault coincides with any unusual smells, noises, or other warning signs.