Chaffoteaux 6P2 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 6P2 fault code mean?
Fault code 6P2 points to the boiler's air pressure switch (APS) failing to confirm adequate airflow during normal operation. When the boiler fires up, the fan runs and creates a pressure differential across the Venturi — a small tube assembly attached to the fan outlet. This pressure change should physically close the APS membrane and send a confirmation signal to the PCB that the fan is working correctly. If that confirmation doesn't arrive in time, or at all, the boiler locks out and displays 6P2 as a safety precaution, preventing gas from reaching the burner without verified airflow. Note that the closely related code 6P1 covers the same APS contact closure delay but triggers during the start-up sequence rather than mid-operation; 6P2 specifically appears when the fault develops while the appliance is already running.
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
- Damaged or partially melted Venturi tube Common
The Venturi tube sits close to the heat exchanger and can soften or develop a small hole if the boiler has overheated — for example, after running with an unfilled or air-locked system. Even a tiny breach lets air escape rather than build pressure, so the APS never closes properly. This is one of the most frequently reported root causes on Chaffoteaux appliances.
- Faulty air pressure switch Common
The rubber diaphragm inside the APS can harden, split, or become stuck over time. Corroded or oxidised electrical contacts inside the switch will also prevent it from signalling correctly even when the diaphragm moves as intended. Either way, the PCB receives no confirmation of airflow.
- Blocked, kinked, or cracked connecting tubes Common
Short rubber hoses link the Venturi to the APS. These can perish, kink, or crack — particularly on older boilers — allowing the pressure signal to bleed away before it reaches the switch. Condensation finding its way into these tubes can also disrupt the pressure reading.
- Fan running weakly or not at all Sometimes
A worn bearing, dust-clogged impeller, or failing motor can all reduce the fan's output below the threshold needed to close the APS. The boiler may appear to start normally but the fan simply cannot generate sufficient pressure differential.
- Blocked or restricted flue Sometimes
Soot, debris, a bird's nest, or ice at the flue terminal can obstruct the exhaust path. This raises back-pressure, disrupts airflow patterns across the Venturi, and can cause the APS to behave erratically — either staying open when it should close, or remaining closed permanently.
- Air locked in the primary heat exchanger Sometimes
After a prolonged period of inactivity, air can accumulate in the heat exchanger. The boiler may overheat briefly on restart, triggering the APS protection circuit and displaying 6P2.
- Wiring or PCB fault Rare
Degraded wiring between the APS and PCB, or moisture ingress into ageing electrical components, can mimic an APS failure even when the switch itself is sound. PCB faults causing incorrect APS signal interpretation are less common but possible.
How to fix it
- Check that your gas supply is on DIY safe
Confirm other gas appliances in your home — a hob or gas fire — are working. If they are not, contact your gas supplier rather than investigating the boiler further.
- Reset the boiler once DIY safe
Press the reset button on the boiler's front panel and wait at least 60 seconds. Do this no more than once or twice. If the boiler locks out again and re-displays 6P2, stop resetting — repeated attempts will not fix the underlying fault and may mask useful diagnostic information for an engineer.
- Check system pressure DIY safe
Look at the pressure gauge; most Chaffoteaux boilers should sit between 1.0 and 1.5 bar when cold. If the needle is below 1 bar, top up via the filling loop following your boiler's user guide. An air-locked, low-pressure system can contribute to the conditions that trigger 6P2.
- Inspect the flue terminal (exterior only) DIY safe
Go outside and visually check the flue outlet is not blocked by leaves, ice, or other debris. Do not probe inside the flue or dismantle any part of the flue system — that work requires a Gas Safe engineer. In winter, a frozen or iced-over terminal is a realistic cause.
- Engineer: inspect and test the Venturi tube and connecting hoses Gas Safe engineer
A Gas Safe engineer will remove the flue elbow to access the Venturi assembly, check for any deformation, melting, or holes, and inspect the rubber pressure tubes for kinks, splits, or blockages. Cleaning the Venturi alone has resolved 6P2 faults in documented cases; if the tube is damaged it will need replacing.
- Engineer: test the air pressure switch Gas Safe engineer
The engineer will remove the APS, clear its ports, and use a multimeter to measure contact resistance while manually actuating the diaphragm. No change in resistance under test confirms a faulty switch that should be replaced.
- Engineer: check and service the fan Gas Safe engineer
The engineer will observe fan operation on start-up, clean the impeller, and check bearing condition. If the fan cannot reach the required speed or pressure output, it will be repaired or replaced as appropriate.
- Engineer: inspect flue and combustion air path Gas Safe engineer
A thorough flue inspection — including checking for soot accumulation, condensate pooling inside the flue, and any structural obstruction — should be carried out. This is especially important if the boiler is older or has not had a recent service.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
If the steps above have not identified and resolved the problem, a Gas Safe registered engineer must carry out further diagnosis. All internal boiler work — including APS replacement, fan replacement, Venturi repair, and any PCB investigation — is notifiable gas work and must not be attempted by an unqualified person.
Parts you may need
- Air pressure switch (APS) · from £35
- Venturi tube / fan Venturi assembly · from £45
- Boiler fan / flue fan assembly · from £120
- APS connecting rubber hoses (set) · from £12
- PCB (printed circuit board) · from £180
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
What is the difference between Chaffoteaux fault codes 6P1 and 6P2?
Both codes point to the air pressure switch failing to close and confirm proper airflow. The distinction is timing: 6P1 appears when the APS does not respond correctly during the initial start-up sequence before the burner fires, while 6P2 appears when the same failure occurs once the boiler is already up and running. In practice they often share the same root causes — damaged Venturi tube, faulty APS, or weak fan — but 6P2 can also indicate that something has changed mid-operation, such as a sudden flue blockage or a fan bearing failing under load.
Can I fix the Chaffoteaux 6P2 fault myself?
A homeowner can safely try one or two resets, check that the gas supply is on, ensure system pressure is between 1 and 1.5 bar, and look for obvious obstruction at the exterior flue terminal. Beyond those checks, 6P2 requires a Gas Safe registered engineer. The Venturi tube, air pressure switch, fan, and associated wiring are all internal components; working on them without Gas Safe registration is illegal and potentially dangerous.
How much does it typically cost to repair a Chaffoteaux 6P2 fault in the UK?
Most people with a 6P2 fault end up paying somewhere between £100 and £350 all in, covering the engineer's time and any parts. A simple APS swap or Venturi clean at the lower end, a full fan replacement or more involved diagnosis at the higher end. If the fault has damaged the PCB, that alone can add £180–£400 on top, but PCB involvement is not common with this particular code. If your Chaffoteaux boiler is over 12–15 years old and needs a fan or PCB, it is worth getting a new boiler quote at the same time, as parts for older Chaffoteaux models can be difficult to source and expensive.
Why does my Chaffoteaux show 6P2 after the boiler has been off for a long time?
After a prolonged period of inactivity, air can become trapped in the primary heat exchanger. When the boiler restarts, this trapped air can cause localised overheating, which in turn can slightly deform the plastic Venturi tube — one of the most commonly reported triggers for 6P2 on Chaffoteaux boilers. Bleeding the system and checking the Venturi condition are the engineer's first steps in this scenario.