Alpha 0E2 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha 0E2 fault code mean?
The 0E2 fault code appears on Alpha boilers when the control board loses confidence in the ionisation signal from the flame sensing probe. In plain terms, the boiler either failed to detect a flame at all or detected one briefly and then lost it, so it shut down as a safety precaution. You may notice the boiler attempting to fire, running for a few seconds, then cutting out — and repeating that cycle every few minutes. This fault sits in the same family as the Alpha E20 and 0A2 codes, all of which relate to flame sensing or ignition failures. Because the boiler is deliberately stopping itself from supplying gas without confirmed flame detection, this is a lockout condition that requires investigation before the boiler can run safely again.
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
- Carbon-fouled ionisation probe Common
Over time, combustion deposits build up on the metal tip of the ionisation probe, insulating it and weakening the electrical signal the control board relies on to confirm a live flame. This is by far the most frequent cause of 0E2 faults and is often resolved during a service by an engineer carefully cleaning the probe with fine emery cloth.
- Damaged or cracked probe Sometimes
The ionisation probe is a delicate component — a thin metal rod held within a ceramic insulator. A knock during a previous repair or service can crack the ceramic, allowing the signal to leak away before it reaches the control board. Even a hairline crack is enough to cause intermittent or permanent loss of the ionisation signal.
- Corroded probe or wiring Sometimes
On older boilers, the probe's metal components can oxidise, raising electrical resistance and degrading the signal. Corroded or damaged wiring between the probe and the PCB can produce the same effect. This is more likely on boilers that have not had a recent annual service.
- Faulty ignition electrodes Sometimes
If the ignition electrodes are worn, cracked, or have an incorrect gap, the spark may not reliably ignite the gas. With no flame actually established, the ionisation probe has nothing to detect and the boiler locks out with 0E2. Electrode condition is checked and adjusted at an annual service.
- Gas supply or gas valve fault Sometimes
An inadequate gas supply — whether due to low pressure, a partially closed service valve, or a faulty gas valve — means the burner cannot sustain a proper flame even if ignition occurs. The probe detects the flame failing almost immediately and triggers the lockout.
- PCB (control board) fault Rare
The PCB interprets the ionisation current from the probe and decides whether a stable flame is present. A failing PCB may misread a perfectly good signal or fail to register it at all. This is typically diagnosed only after the probe, electrodes, wiring, and gas supply have been ruled out.
How to fix it
- Reset the boiler once DIY safe
Press the reset button and allow the boiler to attempt a full restart. A single reset is reasonable if the fault appeared out of nowhere. If the 0E2 code returns promptly, do not keep resetting — repeated lockouts without investigation can mask a developing fault and repeated ignition attempts without a proper flame are not safe.
- Check your gas supply DIY safe
Confirm that other gas appliances in your home — your hob or a gas fire, for example — are working normally. If nothing gas-powered is working, contact your gas supplier rather than a boiler engineer. Also check that the gas isolation valve on the pipe entering the boiler is fully open (handle parallel to the pipe).
- Check boiler system pressure DIY safe
Look at the pressure gauge on the boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it has dropped below 1 bar, top up via the filling loop according to your boiler manual. Low pressure alone is unlikely to cause 0E2, but it is worth ruling out before calling an engineer.
- Have a Gas Safe engineer inspect and clean the ionisation probe Gas Safe engineer
An engineer will remove the ionisation probe, inspect the ceramic insulator for cracks, and clean any carbon deposits from the metal tip. If the probe is old or damaged, replacement is straightforward and usually more cost-effective than repeated cleaning. This single step resolves the majority of 0E2 faults.
- Have the ignition electrodes inspected and tested Gas Safe engineer
While the engineer has the burner accessible, they should check the condition and gap of the ignition electrodes, inspect their lead connections, and replace any electrode showing wear, cracking, or incorrect positioning.
- Have the gas valve tested Gas Safe engineer
If probe and electrode checks do not resolve the fault, an engineer will test the gas valve for correct operation and gas pressure at the burner. A valve that is not opening fully or not closing cleanly is both a cause of flame failure and a safety concern that must only be handled by a Gas Safe registered engineer.
- Have the PCB tested or replaced if all other components are serviceable Gas Safe engineer
If the ionisation probe, electrodes, wiring, and gas supply have all been confirmed as good and the fault persists, the control board is likely the culprit. PCB diagnosis and replacement must be carried out by a qualified engineer and is typically the last resort after all other causes are eliminated.
Parts you may need
- Ionisation / flame sensing probe · from £25
- Ignition electrode · from £30
- Ignition lead / HT lead · from £20
- Gas valve · from £180
- PCB / control board · 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
Can I fix the Alpha 0E2 fault code myself?
You can safely try one boiler reset and check that your gas supply is on, but that is as far as a homeowner should go. The root cause — a dirty or damaged ionisation probe, faulty electrodes, or a gas valve issue — requires a Gas Safe registered engineer to diagnose and repair. Working on gas components without registration is illegal and dangerous.
How much does it cost to fix an Alpha 0E2 fault in the UK?
Most people with a 0E2 fault pay between £120 and £350, which typically covers the engineer's callout, labour, and a replacement ionisation probe or electrodes if needed. If the gas valve needs replacing the cost is usually £150–£300 for the part alone, taking the total higher. A PCB replacement can add a further £180–£400 in parts. If your boiler is over 12 years old and facing a repair bill above around £400, it is worth getting a new boiler quote alongside the repair quote, as a replacement often pays back within a few years through improved efficiency.
Why does my Alpha boiler fire up and then cut out after a few seconds, showing 0E2?
This is the classic symptom of a weak or absent ionisation signal. The boiler ignites the burner successfully, but the ionisation probe cannot confirm a stable flame — usually because carbon deposits on the probe are blocking its electrical signal. The control board then cuts the gas supply as a safety measure. An engineer cleaning or replacing the probe normally resolves this pattern.
Will an annual boiler service prevent the 0E2 fault code?
In most cases, yes. During a standard annual service a Gas Safe engineer will remove and inspect the ionisation probe, clean off any carbon buildup, check the ignition electrodes, and test the gas valve — all the components most likely to cause a 0E2 fault. Keeping up with yearly servicing is the most cost-effective way to avoid unexpected lockouts.