Ariston 6P2 Fault Code: Causes, Fixes & Repair Costs
What does the Ariston 6P2 fault code mean?
The 6P2 code appears on Ariston boilers when the air pressure switch fails to maintain its signal while the boiler is already running — in other words, the fault develops mid-cycle rather than at start-up (which is what the related 6P1 code indicates). The pressure switch is a safety device that monitors the fan's ability to push combustion gases safely up and out through the flue. When the switch loses confidence that airflow is adequate during a heating or hot water call, the boiler cuts out and locks out to prevent dangerous gases building up inside the appliance. The 6P2 code is therefore a mid-operation lockout, whereas 6P1 is a start-up lockout — both point to the same underlying air-pressure-switch circuit, so the diagnostic approach is very similar.
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
- Melted or distorted Venturi tube Common
The Venturi tube creates the pressure differential that operates the air pressure switch. If the boiler has previously overheated — for example, because it was fired up with an air-locked or unfilled system — the lower section of the Venturi tube can distort or develop a small hole. Air is then drawn through that defect rather than through the correct path, so the switch never receives the signal it expects. This is one of the most frequently reported root causes of the 6P2 fault on Ariston appliances.
- Blocked or partially obstructed flue terminal Common
A build-up of debris, bird nesting material, ice, or even heavy condensation around the external flue terminal can restrict exhaust gas flow. This reduces the pressure differential across the switch during a heating cycle, causing it to drop out and trigger the lockout. The symptom often comes and goes with weather conditions.
- Failed air pressure switch Common
Like any electro-mechanical component, the pressure switch itself can wear out or develop an internal fault. If the Venturi tube and flue are both clear, the switch is the next prime suspect. It may read correctly at rest but fail under the small pressure changes generated by the fan during a live heating call, which is consistent with a fault that appears mid-operation rather than at ignition.
- Cracked, kinked, or disconnected pressure switch hose Sometimes
A short rubber or silicone hose connects the Venturi tube to the pressure switch. With age, heat cycling, and vibration, this hose can crack, harden, or simply work loose at one of its barbed connections. Even a pinhole leak is enough to prevent the switch from closing or staying closed during operation.
- Wiring or PCB connection fault Rare
If the wiring loom between the air pressure switch and the PCB is chafed, has a loose connector, or has developed high resistance through corrosion, the signal from the switch can drop during the vibration and heat of normal operation even if the switch itself is fine. In rare cases the PCB input circuit for the pressure switch signal fails, giving the same symptom.
How to fix it
- Check that your gas supply is working DIY safe
Before anything else, confirm that other gas appliances in your home (a gas hob, for example) are working normally. If there is no gas supply to the property, contact your gas network provider rather than the boiler engineer.
- Reset the boiler once or twice DIY safe
Press the reset button (usually marked with a circular arrow or the word 'Reset') and allow up to 60 seconds for the boiler to attempt a restart. If the 6P2 code clears and the boiler runs successfully, monitor it over the next day or two. If the fault returns promptly or persists after two reset attempts, stop resetting — repeated lockouts without diagnosis can mask a worsening problem.
- Visually inspect the external flue terminal DIY safe
From outside your property, look at where the flue exits the wall or roof. Check for obvious blockages such as debris, a bird's nest, ice, or a neighbouring structure that has been built close to the terminal. Do not attempt to probe or unblock the flue yourself — simply note what you see and report it to the engineer.
- Check system pressure on the boiler gauge DIY safe
Glance at the pressure gauge on the boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 0.5 bar, the system may be significantly under-filled, which can contribute to overheating cycles that damage internal components like the Venturi tube. Top up via the filling loop following the boiler's user guide, then re-check and reset.
- Arrange an inspection by a Gas Safe registered engineer Gas Safe engineer
A qualified engineer will need to open the casing and methodically check the Venturi tube for distortion or holes, inspect the rubber pressure switch hose for cracks or loose connections, test the air pressure switch electrically, check fan output, and review relevant wiring and PCB connections. All of this work is inside the appliance and must only be carried out by someone registered on the Gas Safe Register.
- Replace the faulty component identified by the engineer Gas Safe engineer
Depending on diagnosis, the repair will typically involve replacing the Venturi tube, the pressure switch hose, the air pressure switch, or a combination of these. In less common cases the PCB or fan may also need attention. Ensure the engineer tests the boiler through a full heating and hot water cycle before leaving to confirm the fault has been resolved.
Parts you may need
- Air pressure switch · from £55
- Venturi tube assembly · from £45
- Pressure switch connecting hose · from £12
- Flue gas fan (if also found faulty) · from £120
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–£300, depending on the underlying cause.
Frequently asked questions
What is the difference between Ariston fault codes 6P1 and 6P2?
Both codes relate to the air pressure switch circuit, but they trigger at different points in the boiler's cycle. 6P1 means the pressure switch had not closed by the time the boiler tried to ignite — a start-up failure. 6P2 means the switch opened or lost its signal while the boiler was already running — a mid-operation cut-out. The underlying causes (Venturi tube, hose, switch, flue blockage) are broadly the same for both codes, but 6P2 can sometimes point more specifically to a component that fails under sustained heat and pressure rather than one that is permanently stuck.
Can I fix the Ariston 6P2 fault myself?
The initial checks — confirming your gas supply, resetting the boiler once or twice, glancing at the external flue terminal, and topping up system pressure — are perfectly safe for a homeowner to carry out. Beyond that, no. The components involved (Venturi tube, pressure switch, fan, PCB wiring) sit inside the boiler casing. Working on them without Gas Safe registration is both unsafe and illegal under UK gas safety regulations. Always use a Gas Safe registered engineer for the diagnosis and repair.
How much does it typically cost to fix a 6P2 fault on an Ariston boiler?
Most people with this fault pay somewhere between £120 and £300 all-in, depending on which component needs replacing and your location. A straightforward air pressure switch swap with labour usually falls in the £150–£250 range. Replacing the Venturi tube tends to sit toward the higher end, around £200–£300, because it can involve more disassembly. If the fault turns out to be a failed PCB, costs can rise significantly beyond this range — a Gas Safe engineer should give you a firm quote before committing to that repair.
Why does the 6P2 fault only appear after the boiler has been running for a while?
Because the fault develops during operation rather than at start-up, it often points to a component that works initially but fails once it warms up or is exposed to sustained airflow. A Venturi tube with a small crack, a hose that is nearly disconnected, or a pressure switch with a weak internal diaphragm can all pass the initial ignition checks but then lose integrity during a longer heating call. Cold weather can also worsen a marginal flue restriction, so you may notice the fault more frequently in winter.