Andrews A02 Fault Code: Causes, Fixes & Repair Costs
What does the Andrews A02 fault code mean?
The A02 fault code means the boiler's control system is detecting a flame signal even though the burner has been commanded to switch off. This is commonly referred to as a 'spurious' or 'false flame' signal — the ionisation circuit is reporting a flame present when there should be none. Because the boiler cannot safely continue operating in this state, it locks out and requires a manual reset. The two principal causes identified for this code are an ionisation electrode fault (including its wiring and ignition cable) and a PCB (control board) anomaly. Andrews Water Heaters are predominantly commercial and industrial gas-fired appliances, so this fault should always be attended to by a Gas Safe registered engineer familiar with commercial equipment.
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 ionisation electrode Common
The ionisation electrode is the component that senses whether a flame is actually present. If it is cracked, corroded, covered in carbon deposits, or physically misaligned, it can generate a rogue electrical signal that the PCB interprets as a flame — even when the burner is off. This is the most common root cause of an A02 fault on Andrews appliances.
- Damaged ionisation lead or ignition cable Common
The wiring and insulation connecting the electrode to the PCB can deteriorate over time, particularly in the high-temperature environment inside a commercial water heater. Damaged insulation or a loose connection can allow stray current to mimic a flame signal, triggering the A02 lockout without any electrode fault being present.
- Incorrect electrode gap or positioning Sometimes
If the electrode has been disturbed during servicing, or if it has shifted due to vibration in a commercial installation, the gap between the electrode tip and burner may be incorrect. This can cause erratic or persistent signals reaching the PCB even when no combustion is taking place.
- PCB (control board) fault Sometimes
The PCB processes the signal from the ionisation electrode and decides whether a flame is genuinely present. If the board itself is faulty — due to component failure, moisture ingress, or electrical surge — it may misinterpret the input and log a false flame condition. A PCB fault tends to be suspected once electrode checks have been completed and the fault persists.
How to fix it
- Attempt a single manual reset DIY safe
Locate the reset button on the boiler's control panel and hold it as directed in your appliance documentation. Allow the boiler to attempt a restart. If the A02 code clears and the unit runs normally, monitor it closely. Do not reset more than two or three times in total — repeated resets without resolving the underlying fault can cause additional stress to the PCB and will not fix the root cause.
- Check your gas supply is live DIY safe
Confirm that other gas appliances in the building (such as a gas hob or a separate boiler) are working normally. If no gas appliances are functioning, contact your gas supplier rather than an engineer. If gas is available elsewhere, the fault is internal to the Andrews unit.
- Do not attempt to open the appliance casing Gas Safe engineer
The A02 fault is an internal electrical and combustion-related fault. Opening the casing to inspect or touch any components — including the electrode, wiring, or PCB — must only be carried out by a Gas Safe registered engineer. Attempting this yourself is unsafe and will invalidate any remaining warranty.
- Engineer to inspect and clean the ionisation electrode Gas Safe engineer
A Gas Safe engineer will access the electrode assembly, check for carbon fouling, corrosion, or physical cracking, and clean the electrode tip if appropriate. They will also verify the electrode gap and confirm correct alignment with the burner. On commercial Andrews units, the electrode specification and positioning are critical to accurate flame detection.
- Engineer to inspect the ionisation lead and ignition cable Gas Safe engineer
The engineer will check the full length of the wiring from the electrode back to the PCB, looking for cracked insulation, loose connectors, or signs of heat damage. A damaged lead can be replaced independently of the electrode assembly and is a relatively low-cost fix if identified early.
- Engineer to replace the electrode assembly if cleaning does not resolve the fault Gas Safe engineer
If the electrode is found to be cracked, worn, or persistently giving a rogue signal after cleaning, the engineer will fit a new electrode assembly. This typically resolves the A02 fault in the majority of cases.
- Engineer to test and assess the PCB if the fault persists Gas Safe engineer
If a new electrode and confirmed-good wiring still result in an A02 lockout after reset, the PCB is the likely culprit. The engineer will carry out electrical testing of the board. Depending on the findings, the board may be repairable or will need full replacement. Given that Andrews appliances are commercial units, sourcing a compatible board may require going through Andrews Water Heaters directly or an approved parts supplier.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Beyond a single reset, all fault-finding and repair work on an Andrews commercial water heater must be carried out by a Gas Safe registered engineer — ideally one with experience on commercial appliances. You can verify any engineer's registration at gassaferegister.co.uk before authorising work.
Parts you may need
- Ionisation / flame detection electrode · from £35
- Ignition and ionisation lead set · from £45
- PCB (control board) — Andrews commercial unit · from £280
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 £100–£350, depending on the underlying cause.
Frequently asked questions
Is the Andrews A02 fault dangerous?
The A02 code itself is a safety lockout — the boiler has shut itself down because it detected something unexpected. While a false flame signal does not necessarily mean gas is escaping, the boiler should not be repeatedly reset and left running without investigation. Switch the appliance off if it continues to lock out after one or two resets, and arrange for a Gas Safe engineer to attend. Do not ignore a persistent A02 fault.
Can I fix an A02 fault myself?
The only action a non-engineer should take is a single manual reset and checking that the gas supply to the building is live. Everything beyond that — inspecting the electrode, checking wiring, or assessing the PCB — requires a Gas Safe registered engineer. Andrews appliances are commercial water heaters, which makes DIY intervention even less appropriate than on a domestic boiler.
How much does it cost to fix an Andrews A02 fault?
If the cause is a dirty or misaligned ionisation electrode, an engineer visit including inspection and cleaning will typically cost £100–£200. Electrode replacement usually brings the total to around £150–£300 including labour. If the PCB is at fault, costs rise significantly — PCB replacement on commercial Andrews units can reach £450–£700 or more including parts and labour. For that reason, if the appliance is older or out of warranty, it is worth discussing repair-versus-replacement options with your engineer before committing to a board replacement.
Why does my Andrews boiler keep showing A02 after I reset it?
A recurring A02 fault almost always means the underlying cause — a faulty ionisation electrode, damaged wiring, or a malfunctioning PCB — has not been addressed. Resetting the boiler only clears the lockout temporarily; it does not fix the component that is sending the rogue flame signal. Repeated resets without repair are not recommended, as they can place additional strain on the control board. You should arrange for a Gas Safe engineer to carry out a proper diagnosis rather than continuing to reset the unit.