Vokera A11 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera A11 fault code mean?
The A11 code on a Vokera boiler indicates a 'false flame' condition — the boiler's flame detection system is registering a flame signal at a point when the burner should not be alight. Because the control system cannot reconcile an unexpected flame signal with normal operation, it triggers a safety lockout to protect your home. This is not a minor nuisance fault: any fault involving an unexpected flame signal must be taken seriously and investigated by a Gas Safe registered engineer before the boiler is returned to regular use.
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
- Sticking or leaking gas valve Common
The gas valve is responsible for controlling the flow of gas to the burner. If it sticks in a partially open position, gas can continue to reach the burner after it should have shut off, producing a residual flame that the ionisation probe picks up. This is the single most frequent root cause of the A11 fault, and it becomes more common as a boiler ages. A Gas Safe engineer will test the valve's operation and either service or replace it.
- Dirty or degraded flame sensor (ionisation probe) Common
The ionisation probe detects the burner flame by measuring a tiny electrical current through the flame. If the probe tip is coated with combustion deposits, or if the electrode has degraded, it can send erratic or false signals to the PCB — causing the board to believe a flame is present when the burner is off. Cleaning or replacing the probe is a relatively straightforward job for an engineer.
- Faulty PCB Sometimes
The PCB is the boiler's central control board. It receives and interprets the signal from the flame sensor. If the PCB develops a fault — for instance due to a failed component or moisture ingress — it may misread the sensor input and log a false flame even when everything else is working correctly. Because the PCB and the flame sensor can produce identical symptoms, a thorough diagnostic is needed before replacing either part.
- Wiring or electrical interference Sometimes
Damaged, loose, or corroded wiring between the ionisation probe and the PCB can introduce stray electrical signals that mimic a flame detection current. Similarly, poor earthing elsewhere in the boiler circuit can cause interference. An engineer will inspect the wiring loom and connections as part of a systematic diagnosis.
How to fix it
- Switch the boiler off and wait 30 seconds, then attempt a single reset DIY safe
Power the boiler down fully at the programmer or boiler switch, wait about 30 seconds, then press the reset button as described in your Vokera manual. Watch the display — if the A11 code returns within a few minutes, do not reset again. One cautious reset is reasonable; repeated resets on a false-flame fault are not safe and could allow uncontrolled gas flow to go unnoticed.
- If A11 returns immediately, turn off the gas supply DIY safe
If the lockout reappears as soon as the boiler tries to fire, turn off your gas supply at the meter and do not attempt to restart the boiler. Contact a Gas Safe registered engineer straight away. Do not leave the boiler running in this state.
- Call a Gas Safe registered engineer for diagnosis Gas Safe engineer
A qualified engineer will carry out a systematic inspection covering the ionisation probe (cleaning or replacing it if contaminated), the gas valve (checking for sticking, leakage, or wear), the PCB (testing signal outputs and comparing them against expected values), and the wiring harness (looking for corrosion, damage, or poor connections). Do not attempt to inspect or adjust the gas valve or PCB yourself — this work requires Gas Safe registration and specialist equipment.
- Have the faulty component repaired or replaced Gas Safe engineer
Once the engineer has identified the root cause, they will advise on repair or replacement. For older Vokera boilers, ask the engineer to assess the overall condition of other expensive components (heat exchanger, pump, PCB) at the same time — if several parts are showing significant wear, a new boiler may represent better value than investing in multiple repairs.
Parts you may need
- Ionisation probe / flame sensor · from £35
- Gas valve · from £180
- PCB (printed circuit board) · from £280
- Boiler wiring harness / loom · from £60
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
Is the Vokera A11 fault dangerous?
It should be treated as urgent, yes. The boiler has locked out because it detected a flame signal when no flame should be present — which could indicate gas is passing through the valve when it shouldn't be. Do not repeatedly reset the boiler to force it back into operation. Turn off the gas at the meter if the fault returns immediately after a reset, and call a Gas Safe engineer the same day.
Can I reset my Vokera boiler to clear the A11 code?
One careful reset is acceptable — power the boiler off for 30 seconds, then reset and watch what happens. If the A11 code clears and the boiler runs normally, monitor it closely over the next day or two. If the code returns straight away or keeps coming back, stop resetting and call an engineer. Repeated resets on a false-flame fault are not safe.
How much does it cost to fix a Vokera A11 fault?
Most repairs fall in the £120–£380 range, depending on which component is at fault. Replacing the ionisation probe is typically £100–£150 all-in. A gas valve replacement is usually £275–£350 including parts and labour. For a straightforward wiring or connection repair the cost is often towards the lower end. PCB replacement can be significantly more — sometimes £450–£550 — so if the PCB is the cause on an older boiler, it is worth discussing with your engineer whether a new boiler makes more financial sense.
Why is my Vokera boiler showing A11 when there's no demand for heat?
The most likely explanation is that the gas valve is sticking slightly open, allowing a trickle of gas through when the valve should be fully closed. This produces a small residual flame that the ionisation probe detects. A faulty or dirty probe can also send a false signal independently of the valve. Either way, a Gas Safe engineer needs to test both components to identify which is responsible.