Alpha 0A2 Fault Code: Causes, Fixes & Repair Costs
What does the Alpha 0A2 fault code mean?
The 0A2 fault code on Alpha boilers indicates that the boiler has failed to detect a flame during or after the ignition sequence. When the ionisation probe (flame sensor) cannot confirm that a burner flame is present, the boiler shuts down as a safety precaution — cutting the gas supply to prevent unburnt gas from accumulating. This is a hard lockout, meaning the boiler will not restart on its own; the root cause must be identified and resolved before normal operation can resume. The fault sits in the same family as Alpha codes E20 and 0E2, all of which relate to flame detection or ionisation failures, and an engineer will approach them in a similar way.
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
- Dirty or carbon-coated ionisation probe Common
Over time, combustion deposits build up on the tip of the ionisation probe, insulating it and reducing the electrical signal it returns to the PCB. This is the single most common trigger for 0A2. A Gas Safe engineer can clean the probe with fine emery cloth during a service visit, often resolving the fault quickly and at low cost.
- Gas supply interrupted or pressure too low Common
If the mains gas supply has been interrupted — for example, a closed meter cock, a supplier outage, or low incoming pressure — the burner simply won't light and the probe will correctly report no flame. Checking whether other gas appliances in your home are working is a straightforward first step you can do yourself.
- Cracked or failed ionisation probe Sometimes
Hairline cracks in the probe's ceramic insulator allow electrical current to leak to earth rather than return a clean ionisation signal. Cleaning will not fix physical damage — the probe must be replaced. This is still a relatively affordable repair but requires a Gas Safe engineer.
- Loose, corroded, or damaged probe wiring Sometimes
The low-voltage signal from the ionisation probe travels along a dedicated lead back to the PCB. Corrosion at the terminals, a loose connector, or a damaged cable can interrupt that signal and mimic a probe failure. An engineer will check wiring continuity and terminal condition as part of any 0A2 diagnosis.
- Weak ionisation current (probe ageing) Sometimes
A healthy ionisation probe typically generates 2–6 microamps. As probes age, output can fall below 1 microamp — enough for the PCB to reject the signal even though the probe looks physically intact. An engineer can measure this with a microammeter while the boiler fires, confirming whether replacement is warranted.
- PCB (printed circuit board) fault Rare
If the PCB is malfunctioning, it may fail to send the correct ignition signals or misinterpret the feedback from the ionisation probe. PCB faults tend to appear after other causes have been ruled out. Replacement is more expensive and should only be considered once the engineer has confirmed other components are functioning correctly.
How to fix it
- Check that your gas supply is working DIY safe
Test another gas appliance in your home — a gas hob, for example. If it lights normally, your gas supply is fine and the fault is boiler-specific. If no gas appliances are working, contact your gas supplier before calling a boiler engineer.
- Attempt a single boiler reset DIY safe
On most Alpha boilers, rotate the front selector switch to the RESET position, hold for around 30 seconds, then return it to its original setting. If the boiler fires up and runs normally, monitor it over the next hour. If the 0A2 code returns, do not reset again — repeated resets without fixing the cause can mask a developing problem. Move on to calling an engineer.
- Gas Safe engineer: inspect and test the ionisation probe Gas Safe engineer
The engineer will isolate the boiler, remove the casing, and locate the ionisation probe on the burner assembly. They will check the probe visually for cracks or heavy carbon deposits, and use a microammeter to measure the ionisation current while the boiler fires. A reading below around 1 microamp, or visible damage, points clearly to the probe as the cause.
- Gas Safe engineer: clean or replace the ionisation probe Gas Safe engineer
If the probe is simply coated in carbon, the engineer can clean it carefully with fine emery cloth — this is a routine part of an annual service. If there is physical damage or the ionisation current remains low after cleaning, the probe should be replaced with a genuine Alpha-compatible part.
- Gas Safe engineer: inspect probe wiring and connections Gas Safe engineer
The engineer will check the probe lead, connectors, and terminals for signs of corrosion, overheating, or mechanical damage. Any compromised wiring should be repaired or replaced to restore a reliable signal path to the PCB.
- Gas Safe engineer: assess the PCB if all other checks pass Gas Safe engineer
If the probe, wiring, and gas supply are all confirmed to be in good order but the fault persists, the PCB becomes the likely culprit. The engineer may need to carry out further electrical tests before recommending PCB replacement, as this is the most costly repair associated with 0A2.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
If the simple homeowner checks above have not resolved the fault, contact a Gas Safe registered engineer. It is a legal requirement that only Gas Safe registered engineers work on gas appliances in the UK — you can verify an engineer's registration at gassaferegister.co.uk. Do not attempt to remove the boiler casing or inspect internal components yourself.
Parts you may need
- Alpha ionisation probe / flame sensing electrode · from £25
- Ignition electrode (separate from ionisation probe on some models) · from £30
- Probe connecting lead / ignition lead · from £20
- Alpha PCB (control board) · from £250
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 £90–£280, depending on the underlying cause.
Frequently asked questions
Can I keep resetting my Alpha boiler to clear the 0A2 code?
One reset is reasonable — it can clear a transient glitch and tell you whether the fault is persistent. However, if the 0A2 code returns after a reset, stop there. Repeatedly resetting a boiler with an underlying flame sensing fault does not fix the problem and can in some cases cause further wear to the ignition components. Call a Gas Safe engineer to find and fix the root cause.
How much does it cost to fix an Alpha 0A2 fault?
For the most common cause — a dirty or failed ionisation probe — you're typically looking at £90 to £180 all in, covering the engineer's call-out, labour, and any parts. If the wiring needs attention as well, costs may reach around £280. A PCB replacement, which is needed only in a minority of cases, will add significantly more — often £350 to £500 once parts and labour are included — but an engineer should always exhaust cheaper options first. Having your boiler serviced annually (usually £70–£110) reduces the chance of probe faults developing in the first place.
What is the ionisation probe and why does it cause lockouts?
The ionisation probe is a small metal rod positioned in the burner flame. When the flame is lit, it conducts a tiny electrical current (typically 2–6 microamps) back to the PCB, confirming combustion is taking place. If that signal is absent or too weak — because the probe is dirty, cracked, or the flame never formed — the boiler's safety system immediately cuts the gas supply and locks out, displaying 0A2. This is a deliberate safety feature, not a malfunction.
Is the Alpha 0A2 code the same as E20 or 0E2?
They are closely related. All three codes — 0A2, E20, and 0E2 — fall into the flame detection and ionisation fault category on Alpha boilers, and a Gas Safe engineer will investigate them in much the same way: checking the ionisation probe, gas supply, wiring, and PCB. The specific code displayed can depend on the boiler model and at what stage of the ignition sequence the failure occurred, but the diagnostic and repair approach is essentially identical across all three.