Ariston 5P2 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 5P2 fault code mean?
The 5P2 fault code means your Ariston boiler attempted to light the burner twice and failed on both occasions, triggering a full safety lockout. Once in lockout, the boiler will not try again until it is manually reset. On some older Ariston display panels, the digit '5' can closely resemble the letter 'S', so you may see this displayed as 'SP2' — this is exactly the same fault, not a different code. The ignition sequence relies on a chain of components all working together: gas arriving at the correct pressure, the spark electrode firing reliably, the fan proving airflow, and the ionisation electrode confirming a stable flame. If any part of that chain fails twice in a row, the control board shuts everything down for safety and shows 5P2.
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
- Low or interrupted gas supply Common
If gas pressure at the meter is below the required level, or the gas has been temporarily interrupted — for example following utility works in your street, or because the meter valve was accidentally turned — the burner simply cannot light. Check that your gas hob or cooker fires up normally as a quick indicator of whether gas is reaching the property.
- Faulty or dirty ignition / ionisation electrode Common
Over time the ignition electrode accumulates carbon deposits and can crack or wear, preventing it from producing a reliable spark. The ionisation (flame-sensing) electrode can also become coated or misaligned so that even when a flame does appear the boiler's control board cannot confirm it, causing a lockout. This is especially common on boilers that are seven years old or more.
- Frozen condensate pipe Common
In cold snaps, condensate water inside the plastic drain pipe that runs outside the property can freeze solid. This blocks the flue system and prevents ignition. If temperatures have been at or below freezing and the boiler stopped overnight or early morning, this is a strong candidate. Look for ice or frost on the external section of the pipe.
- Blocked or restricted flue Sometimes
A bird's nest, debris, or a build-up of ice around the flue terminal can restrict airflow enough to prevent safe ignition. The boiler's fan-pressure sensor will detect the restriction and the control board will refuse to allow ignition to proceed.
- Faulty fan or spark generator Sometimes
The fan must reach the correct speed and prove adequate draught before ignition is allowed. A fan that is starting to seize, running slowly, or producing inconsistent pressure readings will interrupt the ignition sequence. Similarly, a failing spark generator may not produce a strong enough spark to light the gas reliably.
- Unstable or poor mains power supply Sometimes
Voltage fluctuations or brief power cuts can disrupt the boiler's control board mid-sequence, causing it to log the ignition attempts as failures. If the fault appeared immediately after a power cut or during a storm, this is worth considering.
- Faulty PCB or gas valve Rare
In a small number of cases the printed circuit board (PCB) may be sending incorrect signals to the gas valve, or the gas valve itself may be sticking and not opening fully. These are less common but should be investigated by an engineer if all other causes have been ruled out.
How to fix it
- Check your gas supply using another appliance DIY safe
Before touching the boiler, turn on a gas hob ring or check another gas appliance. If it lights normally, gas is reaching the property. If nothing works, call your gas supplier — do not attempt to reset the boiler. Also confirm the isolation valve at the gas meter is fully open (handle parallel to the pipe).
- Thaw a frozen condensate pipe if temperatures are at or below freezing DIY safe
Locate the plastic condensate drain pipe — usually a white or grey 22 mm pipe exiting the boiler through an outside wall. If it feels solid or is visibly iced over, pour warm (not boiling) water along its length until it runs freely. Once thawed, reset the boiler. After the boiler is running again, lag the pipe with foam insulation to reduce the chance of refreezing.
- Reset the boiler — once or twice only DIY safe
Press and hold the reset button on the boiler's front panel for around five seconds until the display changes. Allow the boiler two full minutes to complete its start-up sequence before concluding whether the fault has cleared. If the 5P2 code returns after two reset attempts, do not keep resetting — repeated failed ignitions can allow unburned gas to accumulate, and continued resets will not fix an underlying component fault.
- If the fault persists, arrange a visit from a Gas Safe registered engineer Gas Safe engineer
A recurring 5P2 lockout points to a fault within the gas, ignition, or flue system that requires professional diagnosis. An engineer will check and set gas inlet pressure, inspect and clean or replace the ignition and ionisation electrodes, examine the spark generator, test the fan and its pressure differential switch, inspect the flue terminal for blockages, and assess the PCB and gas valve. Do not attempt to access or adjust any of these components yourself.
Parts you may need
- Ignition electrode · from £25
- Ionisation / flame-sensing electrode · from £20
- Spark generator / ignition lead · from £35
- Boiler fan (combustion fan) · from £120
- Gas valve · from £130
- PCB (main control board) · from £200
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 £150–£380, depending on the underlying cause.
Frequently asked questions
Is the 5P2 code the same as SP2 on my Ariston boiler?
Yes, exactly the same fault. On certain older Ariston display panels the numeral '5' is rendered in a seven-segment style that can look very much like the letter 'S', so SP2 and 5P2 are one and the same lockout — second ignition attempt failed. Follow the same checks and call an engineer if the problem persists.
How is 5P2 different from 5P1 on an Ariston boiler?
5P1 appears when the first ignition attempt fails. If the boiler then tries a second time and still cannot establish a stable flame, the code upgrades to 5P2 and the boiler locks out completely, requiring a manual reset. In practice both codes point to the same range of causes — gas supply issues, electrode faults, flue problems — but 5P2 indicates the boiler has already given itself a second chance and still could not light, so engineer attention is more likely to be needed.
Can I keep resetting my Ariston boiler to clear the 5P2 fault?
You should limit resets to two or three attempts at most. If the code returns each time, repeated resetting will not cure the underlying fault and can in theory allow unburned gas to collect in the combustion chamber. Note down the code, stop resetting, and call a Gas Safe registered engineer to diagnose the root cause.
How much does it typically cost to fix an Ariston 5P2 fault?
Most people with this fault pay somewhere between £150 and £380 all-in, depending on what has failed. Cleaning or replacing ignition and ionisation electrodes is at the lower end of that range. A fan or gas valve replacement will push towards the higher end. In rare situations where the PCB needs replacing, costs can rise above £400 — if your boiler is older than ten years it may be worth comparing that against the cost of a new boiler rather than investing heavily in repairs.