Vokera AL34 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera AL34 fault code mean?
AL34 is a lockout fault on Vokera boilers, particularly the Mynute VHE series, indicating that the control board is not receiving a valid speed signal from the boiler fan. The fan contains a small tachometer (tacho) sensor that continuously reports its rotational speed back to the PCB. If that signal is absent, too weak, or outside the expected range — whether because the fan is stationary, spinning too slowly, or the signal wire is damaged — the boiler locks out as a safety measure. Because the fan is responsible for expelling combustion gases safely through the flue, the boiler will not attempt to fire without confirmation that it is working correctly.
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
- Worn or seized fan bearings Common
Over time the fan motor's bearings wear down, causing the fan to spin sluggishly or seize entirely. This is the single most frequent cause of AL34. You may notice an unusual grinding or humming noise from the boiler before lockout occurs.
- Burnt-out motor windings Common
The fan motor's internal copper windings can burn out, particularly on older or heavily used boilers. When this happens the motor loses the ability to generate enough torque to reach the speed the PCB expects, triggering the fault.
- Damaged or disconnected tacho wiring Sometimes
The thin signal wire that carries the tacho feedback from the fan to the PCB can become loose at a connector, chafed against a component, or corroded. The fan itself may be physically fine but the PCB receives no signal, producing the same lockout.
- Debris or blockage obstructing the fan Sometimes
Dust, fluff, or occasionally insects can build up around the fan impeller, placing enough load on the motor to slow it below the acceptable threshold. This is more common in boilers installed in dusty utility rooms or cupboards.
- Faulty air pressure switch Sometimes
On some Vokera models the air pressure switch monitors the airflow produced by the fan and forms part of the fan-proving circuit. A failed or sticking diaphragm in the pressure switch can mimic a fan fault by preventing the control sequence from completing, even when the fan is running normally.
- PCB fault Rare
In a small number of cases the PCB itself fails to process the tacho signal correctly, either due to a failed component on the board or a firmware issue. This is usually only suspected once the fan and wiring have been confirmed good.
How to fix it
- Note down the fault code before doing anything else DIY safe
Take a photo of the display showing AL34 or write it down. If the fault recurs after a reset, having a record helps the engineer diagnose the issue faster and may indicate whether it is an intermittent or permanent failure.
- Check that the gas supply to the boiler is on DIY safe
Confirm that the gas isolation valve on the supply pipe to the boiler is in the open position (handle in line with the pipe). Check that other gas appliances in the property, such as the hob, are working normally. If no gas appliances are working, contact your gas supplier rather than resetting the boiler.
- Attempt a single boiler reset DIY safe
Press and hold the reset button (labelled R on most Vokera models) for approximately 3–5 seconds until the fault code stops flashing, then release. Allow the boiler a full minute to complete its start-up sequence. If it fires successfully and runs without returning AL34, monitor it over the next 24 hours. Do not reset the boiler more than two or three times in total — repeated unsuccessful resets will not fix the underlying problem and can mask important diagnostic information.
- If the fault returns, do not attempt further resets — contact a Gas Safe engineer Gas Safe engineer
AL34 requires hands-on investigation of the fan, its wiring, and potentially the PCB. These components sit within the boiler's sealed casing alongside the gas train and heat exchanger. A Gas Safe registered engineer will remove the fan, test the motor windings with a multimeter, inspect the tacho signal wire continuity, and check the air pressure switch. If the fan is confirmed faulty it will almost always need replacing rather than repairing, as labour costs make repair uneconomical.
- Engineer to inspect and test the fan assembly Gas Safe engineer
The engineer will spin the fan by hand to feel for bearing roughness, measure motor resistance across the windings, and verify that the tacho output voltage is within specification under power. A seized or electrically failed fan will be replaced like-for-like with a compatible Vokera part or an approved equivalent.
- Engineer to check tacho wiring and PCB signal integrity Gas Safe engineer
Using a multimeter the engineer will trace the signal wire from the fan connector to the PCB, looking for breaks, high resistance joints, or damaged insulation. If the wiring is intact and the new fan still produces AL34, the PCB may need to be tested or replaced.
- Engineer to inspect for system blockages if overheat-related faults are also present Gas Safe engineer
AL34 sits alongside other lockout codes in the Vokera fault hierarchy. If there are signs of overheating — such as AL10, AL20, or AL21 also appearing — the engineer should check that the circulating pump is running freely, that thermostats and thermistors are reading correctly, and that there are no significant blockages in the system pipework.
Parts you may need
- Vokera boiler fan / fan motor assembly · from £120
- Air pressure switch · from £35
- Tacho signal wiring harness · from £25
- PCB (printed circuit board) · from £180
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 £220–£350, depending on the underlying cause.
Frequently asked questions
Can I fix Vokera AL34 myself?
The safe DIY actions are limited to resetting the boiler once or twice and noting whether the fault clears. The fan, its wiring, and the PCB are all inside the boiler casing alongside gas components, so any further investigation must be done by a Gas Safe registered engineer. Attempting to work on the fan yourself could invalidate your boiler warranty and, if gas pipework is disturbed, create a serious safety hazard.
How much does it cost to fix AL34 on a Vokera boiler?
For the majority of AL34 faults the repair is a fan replacement. Parts typically cost £100–£150 for a compatible fan, and most Gas Safe engineers charge £100–£200 in labour depending on location and how straightforward the job is, giving a common all-in cost of roughly £220–£350. If the fault turns out to be a faulty PCB rather than the fan, PCB replacement can add another £180–£250 in parts on top of labour, pushing the total higher. If your Vokera is more than 10 years old it is worth weighing repair costs against the price of a new boiler.
Why does my Vokera boiler keep showing AL34 after I reset it?
If AL34 comes back every time you reset, the underlying hardware fault has not been fixed — the reset simply clears the lockout temporarily. Worn fan bearings in particular can allow the fan to start occasionally but fail once the motor warms up, causing the fault to return within minutes or hours. Persistent recurrence means a Gas Safe engineer needs to carry out a proper diagnosis rather than relying on further resets.
Is AL34 dangerous — do I need to stop using the boiler immediately?
Yes, you should stop attempting to use the boiler until it has been inspected. The fan's job is to push combustion gases, including carbon monoxide, safely out through the flue. If the fan is not operating correctly, continuing to fire the boiler risks incomplete combustion or flue gas spillage into the property. The boiler's own safety system has already locked it out for this reason. Make sure you have a working carbon monoxide alarm in the property and keep it in place while the boiler is off.