Chaffoteaux 6P1 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 6P1 fault code mean?
The 6P1 fault code indicates that the boiler's control board has detected a delay or failure in the combustion air pressure switch (also called the combustion products pressure relay). In plain terms, the boiler cannot confirm that the fan is generating sufficient airflow and flue draught to remove exhaust gases safely before ignition begins. As a protective measure, the boiler locks out rather than attempt to fire. Some sources also describe 6P1 as a combustion parameter fault, meaning the boiler's electronics have detected that the burner's combustion settings are outside safe limits — either way, the root cause nearly always involves the fan, flue path, or the pressure switch circuit itself.
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
- Blocked or restricted flue Common
Soot, debris, bird nests, or ice build-up in the flue terminal can restrict the exhaust path, reducing draught to below the level the pressure switch expects. In winter, ice formation at the flue outlet is a particularly common trigger for this fault code.
- Faulty or degraded air pressure switch Common
The pressure switch membrane can become clogged, stiff, or split over time. The small rubber or plastic tubes connecting the switch to the fan housing can also crack, kink, or pull loose, preventing the switch from registering correct pressure and causing it to fail to operate in time.
- Fan failure or reduced fan output Common
If the fan motor is worn, its bearings are degrading, or the impeller is coated in dust and debris, it will not spin at the correct speed or generate sufficient airflow. The pressure switch will not detect the expected pressure differential and the boiler will fault before attempting ignition.
- PCB relay fault Sometimes
The relay on the printed circuit board that controls the flue fan can develop an internal short-circuit or fail to energise properly. This prevents the fan from receiving the correct power signal, which in turn stops the pressure switch from operating. Either the relay component or the full PCB may need replacement.
- Excessive or incorrectly installed flue run Sometimes
Flue pipework that is too long, has too many bends, or has an insufficient internal diameter will cause a permanent loss of draught. This is more common in older installations or where modifications have been made without proper design checks.
- Electrical supply voltage fluctuations Rare
Voltage spikes or an unstable mains supply can cause the pressure relay not to switch within the expected time window, triggering a 6P1 fault even when the fan and flue are physically sound.
How to fix it
- Reset the boiler once DIY safe
Locate the reset button on your Chaffoteaux boiler (typically a dedicated button on the front panel), press it once, and wait for the boiler to attempt a restart. If the fault clears and the boiler fires successfully, monitor it over the next hour. If 6P1 returns, do not repeatedly reset — further resets will not fix an underlying fault and may mask a safety issue.
- Check for an obvious flue blockage or ice DIY safe
Go outside and inspect the flue terminal. Look for any visible obstruction such as a bird nest, accumulated soot, or ice around the outlet. In freezing weather, ice is a common cause — carefully pouring warm (not boiling) water over an iced flue terminal can restore airflow. Do not attempt to reach inside the flue or modify any pipework.
- Check your gas supply DIY safe
Confirm that other gas appliances in your property (cooker, gas fire) are working normally. If no gas appliances are working, contact your gas supplier. If only the boiler is affected, the issue is likely mechanical or electrical rather than a gas supply problem.
- Inspect the pressure switch connecting tubes (engineer) Gas Safe engineer
A Gas Safe engineer should remove and visually inspect the small rubber tubes linking the air pressure switch to the fan and Venturi housing. Cracked, kinked, or disconnected tubes are a common and straightforward fix. The engineer should also blow through the pressure switch ports and listen for the characteristic click that confirms the diaphragm is moving freely, and verify switch resistance with a multimeter.
- Clean the fan impeller and fan housing (engineer) Gas Safe engineer
The engineer should remove the fan assembly and clean the impeller blades and housing of any dust, debris, or condensate residue. Fan bearings should be checked for noise or roughness. If the fan is not reaching the correct speed, drawing insufficient current, or showing physical wear, it should be replaced with a manufacturer-approved part.
- Inspect and clean the flue system (engineer) Gas Safe engineer
The engineer should carry out a full flue integrity check, including measuring draught at the terminal and inspecting the internal diameter and routing of the flue run. Any sections with excessive horizontal length, inadequate fall, or partial blockage should be rectified. If the flue is structurally damaged, it must be replaced.
- Test or replace the air pressure switch (engineer) Gas Safe engineer
If the tubes and fan are found to be in good order, the engineer should test the pressure switch electrically and replace it if it is not switching correctly at the expected pressure differential. This is a relatively straightforward part replacement on most Chaffoteaux models.
- PCB inspection and relay replacement (engineer) Gas Safe engineer
If the fan, pressure switch, flue, and connecting tubes have all been checked and found serviceable, the fault may lie with the PCB relay that drives the fan circuit. An engineer can test the relay with a multimeter and, where possible, replace just the relay component. If the board is beyond economic repair, a full PCB replacement will be required.
- Combustion analysis and parameter check (engineer) Gas Safe engineer
Where 6P1 is being interpreted as a combustion parameter fault rather than a purely mechanical airflow issue, the engineer must use a calibrated flue gas analyser to measure CO, CO₂, and O₂ levels. Any combustion settings adjustments must only be carried out by a Gas Safe registered engineer — attempting to alter these parameters yourself is illegal and dangerous.
- Call a Gas Safe registered engineer Gas Safe engineer
If the fault has not resolved after the homeowner checks above, or if you have any doubt about the cause, contact a Gas Safe registered engineer. You can verify registration at gassaferegister.co.uk. All gas work on your boiler must be carried out by a registered engineer to comply with UK Gas Safety Regulations.
Parts you may need
- Air pressure switch (combustion products relay) · from £45
- Flue fan / circulation fan assembly · from £120
- Pressure switch connecting tubes (hose kit) · from £15
- Printed circuit board (PCB) · from £200
- Flue terminal kit (horizontal) · from £55
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–£400, depending on the underlying cause.
Frequently asked questions
Is the Chaffoteaux 6P1 fault dangerous?
The boiler has locked out specifically to prevent unsafe operation, so you are not in immediate danger — the burner has not fired. However, you should not attempt to bypass the lockout or reset the boiler more than once or twice. If you smell gas at any point, do not touch any switches, open windows, leave the property, and call the National Gas Emergency Line on 0800 111 999.
Can I fix a 6P1 fault myself?
Homeowners can safely check for an obvious flue blockage or ice at the terminal, confirm the gas supply is working, and attempt a single reset. Everything beyond that — testing the pressure switch, cleaning the fan, inspecting the PCB, or adjusting combustion settings — must be carried out by a Gas Safe registered engineer. Attempting gas appliance repairs yourself without registration is illegal in the UK and could invalidate your home insurance.
How much will it cost to repair a Chaffoteaux 6P1 fault?
For the most common fixes — pressure switch replacement, fan cleaning, or blocked flue clearance — most homeowners pay between £150 and £400 including parts, labour, and call-out. A fan replacement with parts and fitting typically falls in the £250–£380 range. If the PCB needs replacing, costs can rise to £350–£500 or more, so it is worth getting a quote before committing to the repair on an older boiler.
Why does my Chaffoteaux boiler keep showing 6P1 after I reset it?
Repeated 6P1 faults after resetting almost always mean there is an underlying fault that the reset cannot clear — most commonly a deteriorating fan, a partially blocked flue, a failing pressure switch, or a cracked connecting tube. Persistent lockouts need a proper diagnosis by a Gas Safe engineer. Repeatedly resetting without investigation risks masking a developing fault and, in rare cases, can stress other boiler components.
Could a 6P1 fault be caused by cold or freezing weather?
Yes. Ice forming at or around the flue terminal is a well-known winter cause of 6P1 on Chaffoteaux boilers. The ice restricts exhaust gas flow, the pressure switch cannot detect adequate draught, and the boiler locks out. Carefully applying warm water to the iced terminal can resolve this. If the fault keeps returning each winter, an engineer should review the flue terminal position and orientation to reduce the risk of ice build-up.