Ariston A01 Fault Code: Ignition Failure Causes and Safe Checks
Estimated reading time: 6 minutes
The Ariston A01 fault code means the boiler has failed to establish or confirm a burner flame within the permitted ignition time. The boiler then shuts off the gas supply and enters a safety lockout.
A01 is commonly associated with older Ariston Microgenus, Microgenus II and Microgenus HE boilers. Possible causes include an interrupted gas supply, faulty ignition or detection electrodes, damaged ignition leads, a gas-valve problem or a PCB fault.
Check that the property has a working gas supply and try one reset. If A01 returns, contact a Gas Safe registered engineer.
Quick Answer
Ariston error code A01 indicates ignition failure.
The boiler has attempted to light the burner but has not detected a stable flame within the safety period. Ariston’s Microgenus II manual describes A01 as “no flame after safety time”, while the Microgenus HE user manual states that the boiler shuts off the gas if the burner does not ignite.
Which Ariston Boilers Display A01?
The A01 format is mainly found on older Ariston boiler ranges, including certain:
Microgenus models
Microgenus II models
Microgenus HE models
Newer Ariston boilers may use codes such as 501, 5P1 or 5P2 for related ignition and flame-detection problems. Always check the user or servicing manual for the exact boiler model before diagnosing the fault or ordering parts.
What Happens During an A01 Fault?
When the boiler receives a demand for heating or hot water, its electronic controls begin the ignition sequence.
The boiler must:
Establish the correct operating conditions.
Generate a spark through the ignition electrodes.
Open the gas valve.
Ignite the burner.
Confirm the flame through the detection electrode.
If no flame is confirmed within the permitted safety time, the boiler closes the gas valve and displays A01. On Microgenus II models, the manual identifies this safety period as approximately seven seconds.
A01 identifies the result of the problem, but it does not confirm which part has failed.
Possible Causes of Ariston A01
| Possible causes | Why it may triggers Ariston A01 | Who should investigate |
| Interrupted gas supply | The burner cannot ignite if gas is not reaching the boiler. | Homeowner |
| Prepayment meter out of credit | The property may have no active gas supply. | Homeowner |
| Low or unstable gas pressure | The boiler may not receive enough gas to establish a reliable flame. | Gas Safe engineer |
| Ignition electrode fault | A weak, misplaced or missing spark may prevent the burner from lighting. | Gas Safe engineer |
| Flame-detection electrode fault | The burner may light, but the boiler may not recognise the flame. | Gas Safe engineer |
| Damaged ignition lead or wiring | The spark or flame-detection signal may not reach the correct component. | Gas Safe engineer |
| Spark-generator fault | The boiler may not produce the electrical output required for ignition. | Gas Safe engineer |
| Gas valve fault | The gas valve may not open or regulate gas correctly during ignition. | Gas Safe engineer |
| Burner or combustion problem | The burner may fail to light evenly or maintain a stable flame. | Gas Safe engineer |
| Poor electrical earth or polarity | An electrical problem may interfere with spark generation or flame detection. | Gas Safe engineer |
| PCB fault | The PCB may not control ignition or process the flame signal correctly. | Gas Safe engineer |
Microgenus II documentation shows that the ignition system includes separate ignition electrodes, a detection electrode, spark generator, gas valve and PCB connections. Any of these areas may require testing when A01 persists.
Safe Checks for Homeowners
Do not remove the boiler casing or attempt to clean electrodes, test wiring or inspect the gas valve.
Check the gas supply
Check whether another gas appliance, such as a gas hob, is working. If no gas appliances work, the problem may relate to the property’s gas supply rather than the boiler.
Where a prepayment meter is installed, confirm that it has credit and is not displaying a supply error. If you smell gas, do not attempt to reset or operate the boiler.
Reset the boiler once
Follow the reset instructions in the user manual for the exact model.
On Microgenus HE models, the manual instructs the user to press and release the reset button after A01 appears. If the boiler fails to ignite again, it recommends checking the external gas supply and arranging professional assistance if the problem continues.
Try one reset only. Repeated resets will not repair a faulty electrode, gas valve, spark generator or PCB.
Should You Check the Boiler Pressure?
Boiler pressure is not the main check for an A01 ignition fault. On Microgenus HE and Microgenus II boilers, insufficient water pressure or circulation is identified separately as E02. A01 specifically relates to the failure to establish or detect a flame.
Pressure should only become part of the investigation if another warning is displayed or the model manual specifically requires it.
What Should a Gas Safe Engineer Check?
The engineer should follow the fault-finding procedure for the exact Ariston model. Checks may include:
Gas availability and working pressure
The complete ignition sequence
Spark-generator operation
Ignition-electrode condition and position
Detection-electrode condition and ionisation signal
Ignition and detection leads
Electrical polarity and earth continuity
Gas-valve power supply and operation
Burner condition
Wiring connections
PCB ignition outputs and flame-signal processing
An important distinction is whether the burner fails to light or lights briefly before A01 appears.
If the burner lights and then shuts down, the problem may be related to flame detection rather than spark generation. A forum example describes a Microgenus boiler lighting successfully but displaying A01 because the flame was apparently not being recognised; however, this type of report should be treated as diagnostic context rather than proof that the PCB is faulty.
Gas boiler repairs must be carried out by an engineer who is Gas Safe registered and qualified for boiler work.
Parts That May Be Related
Depending on the engineer’s diagnosis, related parts may include:
Ignition electrodes
Flame-detection or ionisation electrodes
Electrode leads
Spark generators
Gas valves
Wiring harnesses
Printed circuit boards
Burner components
Do not replace a PCB or gas valve based only on the A01 code. Proper testing is required first.
Find Ariston Boiler Electrodes
Frequently Asked Questions
Yes. Check that the gas supply is working and try one reset according to the boiler manual. Contact an engineer if A01 returns.
Not necessarily. The electrode is one possible cause, but the gas supply, detection electrode, spark generator, gas valve, wiring or PCB may also be responsible.
The flame may be forming but not being detected correctly. An engineer may investigate the detection electrode, its lead, electrical earth and PCB flame-signal circuit.
No. Accessing it requires opening the boiler and working around gas and combustion components. This should be completed by a Gas Safe engineer.
They are both related to ignition or missing flame detection, but they are used on different Ariston boiler generations. Check the manual for the exact model.
Key Takeaways
- The Ariston A01 fault code indicates ignition failure due to the lack of a stable burner flame within the safety period.
- Common causes include interrupted gas supply, ignition electrode faults, and gas valve issues.
- Homeowners can check the gas supply and reset the boiler, but should contact a Gas Safe engineer if the issue persists.
- Gas Safe engineers should investigate the complete ignition sequence and check parts like electrodes, wiring, and valves.
- Avoid replacing parts based solely on the A01 code; proper testing by a qualified engineer is essential.
