Vokera E042 Fault Code: Causes, Fixes & Repair Costs
What does the Vokera E042 fault code mean?
The E042 code appears when the boiler's control system detects a flame signal at a time when the burner should not be alight — either before ignition has been commanded or after the gas supply should have cut off. Because this is a combustion-safety concern (the boiler cannot confirm it is in a safe state), it locks out immediately. A single reset attempt is reasonable, but if the fault returns the boiler must stay off until a Gas Safe registered engineer has inspected it. This is not a fault that can be diagnosed or repaired by a homeowner.
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
- Faulty or contaminated flame-sensing electrode Common
The ionisation electrode sits in the burner assembly and sends a tiny electrical current to the PCB to confirm a flame is present. If the electrode tip is coated in combustion deposits, cracked, or has drifted out of position, it can continue to pass a residual signal to the board even when no flame exists, triggering E042.
- Gas valve not seating fully closed Common
When the boiler shuts down, the gas valve must close completely to stop gas flow. If the valve seat is worn, debris-contaminated, or the solenoid is sticking, a small amount of gas can continue to trickle into the burner, sustaining a residual flame that the sensor correctly — or incorrectly — detects. This is a gas-safety concern and requires immediate engineer attention.
- Damaged or loose wiring to the flame sensor Sometimes
A chafed cable, corroded connector, or loose terminal on the flame-sensor circuit can allow stray electrical signals to reach the PCB, mimicking a genuine flame signal. The fault may appear intermittently and can be difficult to reproduce on the bench.
- Faulty PCB Sometimes
The PCB interprets the signal from the ionisation electrode. If the relevant input circuit on the board has failed or is drifting, it may report a phantom flame even when the electrode itself is serviceable. PCB faults tend to appear after the more straightforward components have been ruled out.
- Flue gas recirculation Rare
If combustion products from the flue outlet are being drawn back towards the air intake — for example due to a poorly positioned or damaged flue terminal — trace amounts of ionised gas can occasionally fool the sensor into reporting a flame signal when none exists.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button (labelled R on most Vokera Vision Plus models) and press and hold it for approximately 3–5 seconds until the fault code stops flashing, then release. On dial-operated models, turn the selector to the Reset or Off/Reset position and hold briefly. Allow the boiler to complete its start-up sequence. Do not reset more than two or three times in total — repeated resets without a successful start can mask a worsening fault.
- Check your gas supply DIY safe
Confirm that other gas appliances in your home (hob, gas fire) are working normally. If nothing gas-powered is working, there may be a supply interruption — contact your gas supplier. If only the boiler is affected, the gas supply to the boiler is likely fine and the fault lies within the appliance itself.
- If you smell gas, act immediately DIY safe
Do not attempt any further resets or inspections. Turn off the gas at the meter, open windows to ventilate the property, avoid operating electrical switches, leave the building, and call the National Gas Emergency Service on 0800 111 999. Only return when cleared to do so by a professional.
- If the fault clears but returns, stop resetting and call an engineer DIY safe
A fault that keeps coming back after a reset indicates an underlying component problem. Continuing to reset will not fix it and could mask a developing safety issue. Leave the boiler off and arrange for a Gas Safe registered engineer to attend.
- Gas Safe engineer: inspect and test the flame-sensing electrode Gas Safe engineer
The engineer should remove the electrode, check for sooting or cracking, measure the ionisation current with the burner running and immediately after shutdown, and replace the electrode if it is not producing a clean signal. This is the most common fix for E042.
- Gas Safe engineer: test the gas valve for leakage and correct closure Gas Safe engineer
Using appropriate test equipment, the engineer should verify that the gas valve closes fully on shutdown and is not letting gas bypass the seat. A leaking or sticking valve must be replaced — it cannot be safely repaired in situ.
- Gas Safe engineer: inspect wiring and connectors on the flame-sensor circuit Gas Safe engineer
The engineer should check the entire cable run from the electrode to the PCB, looking for chafing, heat damage, corrosion, or loose push-fit connectors. Faulty wiring is a low-cost fix if caught early.
- Gas Safe engineer: assess PCB if all other components test satisfactory Gas Safe engineer
If the electrode, valve, and wiring all check out, the PCB's flame-detection input circuit is the likely culprit. The engineer may use a known-good electrode to test the board's response and, if the board is confirmed faulty, arrange a replacement.
- Call a Gas Safe registered engineer DIY safe
If you have not already done so, book a Gas Safe registered engineer to diagnose and repair the fault. You can verify any engineer's credentials at www.gassaferegister.co.uk. Do not run the boiler in a lockout state or attempt to bypass the fault code.
Parts you may need
- Flame-sensing (ionisation) electrode · from £35
- Electrode gasket / seal kit · from £8
- Gas valve (Vokera Vision Plus compatible) · from £205
- PCB (Vokera Vision Plus series) · from £220
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–£350, depending on the underlying cause.
Frequently asked questions
Is E042 dangerous — should I turn the boiler off?
Yes, treat it with caution. The code means the boiler detected a flame when it should not have, which is a combustion-safety issue. Try a single reset; if the fault returns, turn the boiler off and leave it off until a Gas Safe engineer has investigated. If you smell gas at any point, turn off the gas at the meter and call the National Gas Emergency Service on 0800 111 999 immediately.
Can I fix Vokera E042 myself?
Only a single reset attempt is within homeowner territory. Everything beyond that — testing the ionisation electrode, checking the gas valve, or inspecting the PCB — must be carried out by a Gas Safe registered engineer. Working on gas components without the correct registration is illegal and dangerous.
How much does it typically cost to fix E042?
For the two most common causes — a worn flame-sensing electrode or a sticking gas valve — most people pay between £120 and £350 including parts and labour. A straightforward electrode swap with a single call-out will be towards the lower end; a gas valve replacement sits in the middle. If the PCB turns out to be faulty, costs can rise to £400–£500 or more, but PCB failure is a less common diagnosis for this particular code. Always get a written quote before authorising any work.
Why does E042 keep coming back after I reset it?
A fault that clears on reset but reappears within minutes or hours almost always points to a component that is on the verge of failure rather than a one-off glitch. The most likely culprits are a flame-sensing electrode that is heavily sooted or cracked, or a gas valve that is not sealing cleanly. Each time the boiler fires, the underlying problem re-triggers the safety shutdown. Repeated resetting will not solve it — an engineer needs to identify and replace the failing part.