Chaffoteaux 725 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 725 fault code mean?
Fault code 725 on a Chaffoteaux boiler most likely relates to a fan or air pressure circuit fault — the boiler's control board has detected a problem with the flue fan operation or the air pressure switch that monitors it. Chaffoteaux organise their fault codes by functional unit, so '7xx' codes on models that carry a display (such as the Talia, Expert, Calydra and Minima HE ranges) typically point to combustion air-management components. When this code appears, the boiler locks out as a safety measure to prevent unburnt gases building up. Note: Chaffoteaux fault codes are not universal across their full product range — older models such as the Britony Combi SE use LED flash sequences rather than numeric codes, and the exact meaning of 725 can vary by model year. Always cross-reference with your specific model's manual and, if in any doubt, have a Gas Safe registered engineer read the full fault history from the boiler's diagnostic menu.
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 seized flue fan Common
The fan turbine can accumulate debris or suffer bearing wear over time. If it cannot reach the correct speed, the air pressure switch never confirms adequate flue draw and the PCB triggers a lockout. This is the single most common root cause of fan-circuit codes on Chaffoteaux boilers.
- Faulty or stuck air pressure switch Common
The air pressure switch is a small diaphragm device that confirms the fan is moving enough air before ignition is allowed. A faulty diaphragm, blocked pressure-sensing tube, or stuck contact means the PCB receives the wrong signal — either the switch stays open when it should close, or fails to reset after a run cycle.
- Loose or corroded wiring to the fan or pressure switch Common
The fan creates constant vibration, which can gradually loosen push-fit connectors or corrode terminal pins. A poor electrical connection causes intermittent or absent feedback signals to the PCB, producing a spurious fan-circuit lockout even when the fan itself is mechanically sound.
- Frozen or blocked condensate pipe Sometimes
In cold weather, condensate can freeze in the external section of the pipe, causing back-pressure that disrupts flue-gas flow. The resulting pressure fluctuation can confuse the air pressure switch and trigger a fan-related fault code. More likely in winter months or when the condensate pipe lacks lagging.
- PCB sending incorrect signals to the fan circuit Sometimes
If the PCB's fan-control relay or driver circuit develops a fault, it may fail to energise the fan correctly or misinterpret the returning signal. This tends to produce the same 7xx lockout symptom but requires more in-depth diagnosis to distinguish from a straightforward fan or pressure-switch failure.
How to fix it
- Check whether other gas appliances in the property are working DIY safe
Turn on a gas hob or check a gas fire if you have one. If no gas appliances work, the issue may be with your gas supply rather than the boiler. Contact your gas supplier before doing anything else.
- Reset the boiler once DIY safe
Locate the reset button on your Chaffoteaux boiler (usually a dedicated button or a hold-down sequence on the control panel — check your model's quick-start guide). Press it once and wait up to two minutes for the boiler to attempt a restart. If the fault clears and the boiler runs normally, monitor it over the next 24 hours. Do not reset more than two or three times in total; repeated resets on some Chaffoteaux models can trigger a deeper lockout that requires engineer intervention to clear.
- Check for a frozen condensate pipe (winter months only) DIY safe
The condensate pipe is typically a white or grey plastic pipe (22 mm or 32 mm) running from the boiler to an external drain or soakaway. If the outdoor section feels solid or shows ice, carefully pour warm (not boiling) water along the pipe to thaw it, working from the boiler end outward. Once thawed, reset the boiler. Lag the pipe afterwards with foam pipe insulation to reduce the risk of re-freezing.
- Check boiler system pressure DIY safe
Look at the pressure gauge on the boiler front panel. Normal operating pressure is typically 1–1.5 bar when cold. If it reads below 0.8 bar, top it up using the filling loop (refer to your model's manual for the correct procedure). Low pressure alone is unlikely to cause a 725 fault, but it is a quick check worth doing before calling an engineer.
- Inspect the fan and air pressure switch (engineer task) Gas Safe engineer
A Gas Safe registered engineer will remove the boiler casing, visually inspect the fan for debris or bearing damage, and spin-test it. They will also check the pressure-sensing tube connecting the fan housing to the air pressure switch for blockages or splits, and test the switch itself with a multimeter to confirm correct operation across the expected pressure range.
- Check and reseat all wiring connections to the fan and pressure switch (engineer task) Gas Safe engineer
The engineer will inspect every connector in the fan-circuit wiring loom — including the fan motor, the air pressure switch, and the relevant PCB terminals — for signs of corrosion, heat damage, or poor seating. Loose connectors are re-crimped or replaced; corroded terminals are cleaned or the harness section is renewed.
- Replace faulty components as required (engineer task) Gas Safe engineer
Depending on diagnosis, the engineer will replace the fan assembly, the air pressure switch, or both. Parts must be manufacturer-approved replacements to preserve any remaining warranty and ensure correct operation. The engineer will clear the fault code and run a full commissioning check — including a flue-gas analysis — before signing off the repair.
- PCB assessment if fan and pressure switch test satisfactory (engineer task) Gas Safe engineer
If the fan and air pressure switch both check out correctly but the 725 fault persists, the engineer will test the PCB's fan-control relay and driver outputs. A confirmed PCB fault will require replacement of the control board. Given the cost involved, the engineer will also advise on the boiler's age and whether repair or replacement represents better value.
- Call a Gas Safe registered engineer if the fault has not cleared after the homeowner checks above Gas Safe engineer
If resetting once or twice and thawing the condensate pipe (if applicable) have not resolved the lockout, contact a Gas Safe registered engineer and quote fault code 725 along with your exact boiler model name and age. Do not continue attempting resets — have the boiler properly diagnosed.
Parts you may need
- Flue fan assembly (model-specific) · from £95
- Air pressure switch · from £35
- Pressure-sensing tube / hose · from £12
- Fan wiring harness / connector set · from £20
- PCB (control 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 £180–£400, depending on the underlying cause.
Frequently asked questions
Is fault code 725 listed in the Chaffoteaux manual?
Code 725 does not appear in all publicly available Chaffoteaux manuals — Chaffoteaux's fault code structure varies significantly between model ranges and production years. Older models such as the Britony Combi SE use LED flash sequences rather than numeric display codes, while newer models like the Talia and Expert use structured numeric codes organised by functional unit. If you cannot find 725 in your model's own manual, the most reliable next step is to have a Gas Safe engineer connect a diagnostic tool and read the full fault code from the boiler's internal log, which will give a definitive description for your specific model.
Can I fix a Chaffoteaux 725 fault myself?
There are a couple of checks any homeowner can safely carry out: confirming the gas supply is on, attempting a single boiler reset, and thawing a frozen condensate pipe if cold weather is a factor. Beyond that, the likely causes — a faulty fan, air pressure switch, wiring fault, or PCB — all require removal of the boiler casing and work on internal components. Under UK Gas Safe regulations, this work must only be carried out by a Gas Safe registered engineer. Attempting it yourself is both a legal issue and a genuine safety risk.
How much does it typically cost to repair a Chaffoteaux 725 fault in the UK?
Most homeowners with a fan or air pressure switch fault pay somewhere between £180 and £400 all-in, covering the engineer's call-out, labour, and parts. A straightforward air pressure switch replacement sits at the lower end of that range, while a full fan assembly replacement with labour typically falls in the middle. If the fault turns out to be a PCB failure, repair costs can reach £450–£550 or more, and on an older boiler that is approaching 12–15 years of age, a full boiler replacement may represent better long-term value than an expensive PCB repair.
Why does my Chaffoteaux keep locking out with the same code after resetting?
A fault code that returns after one or two resets almost always indicates an underlying component failure rather than a one-off glitch. Repeatedly resetting a locked-out boiler without addressing the root cause can mask the problem, accelerate wear on the fan or ignition components, and on some Chaffoteaux models can trigger a deeper lockout that requires a diagnostic tool to clear. If the code reappears after a reset, stop resetting and arrange for a Gas Safe engineer to carry out a proper diagnosis.