Chaffoteaux 415 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 415 fault code mean?
Fault code 415 appears on Chaffoteaux boilers with a digital display (such as the Talia, Pigma, Inoa and Serelia ranges) and points to a problem within the zone ambient or temperature probe circuit. Chaffoteaux uses a structured fault-code system where the leading digit identifies the affected subsystem: codes in the 4xx series relate to external electronics, zone control boards, and zone temperature sensors. Following the documented 411–416 zone probe sequence — where 411 flags a missing Zone 1 ambient probe and 412 a Zone 2 probe fault — code 415 is consistent with a Zone 5 ambient or flow temperature probe that the PCB cannot read correctly. The probe (an NTC thermistor) works by varying its electrical resistance as temperature changes; when it fails, goes open-circuit, or short-circuits, the boiler loses the temperature data it needs to operate safely and shuts down. Note: Chaffoteaux fault-code numbering differs across model generations and older models (e.g. the Britony) used LED flash sequences rather than numeric codes, so 415 as a discrete display code applies only to digital-display models.
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
- Failed NTC thermistor / temperature probe Common
The NTC probe itself has broken down internally. A healthy thermistor changes resistance smoothly as temperature rises and falls; a failed one returns a resistance of zero (short circuit) or infinity (open circuit), both of which trigger the 415 fault. Because these sensors are inexpensive components that work continuously, age-related failure is the most frequent root cause.
- Loose, corroded or damaged wiring Common
The thin wiring connecting the zone probe to the PCB is vulnerable to corrosion, chafing against the boiler casing, or connector pins working loose over time. Even a high-resistance connection can produce the same open-circuit reading as a dead probe, sending the boiler into lockout.
- Short circuit in the probe circuit Sometimes
A pinched or water-damaged cable can cause the probe wiring to short to earth or to another conductor, making the PCB see an implausible resistance value. This often produces an intermittent fault that clears on reset but returns under load.
- Faulty main PCB Rare
If a replacement probe and fresh wiring both fail to clear the code, the PCB's input circuit for that zone may have developed a fault — damaged tracks, a burned component, or a failed analogue input channel. PCB faults are less common but should be suspected when all other causes have been ruled out.
How to fix it
- Perform a single boiler reset DIY safe
Locate the reset button on your boiler's control panel (usually a flame or spanner symbol) and hold it for the number of seconds specified in your user guide. Allow the boiler a full minute to attempt a restart. If the fault clears and stays clear, monitor the boiler over the next few hours. If fault code 415 returns, do not keep resetting — repeated resets will not cure a probe or wiring fault and may mask a developing problem.
- Check your gas supply DIY safe
Confirm that other gas appliances in the property (hob, fire) are working normally. If they are not, the issue may be with your gas supply rather than the boiler — contact your gas supplier. If gas is available elsewhere, the supply to the boiler is unlikely to be the cause.
- Check system pressure DIY safe
Look at the pressure gauge on the boiler fascia. For most Chaffoteaux combi and system boilers the cold-system pressure should sit between 1.0 and 1.5 bar. If it reads below 1 bar, repressurise via the filling loop following the instructions in your user guide, then attempt one further reset. Low pressure alone will not cause a 415 code, but it is worth correcting before an engineer visits.
- Contact a Gas Safe registered engineer for diagnosis Gas Safe engineer
All work beyond the checks above must be carried out by a qualified engineer. They will use a multimeter in resistance-measurement mode to test the NTC thermistor against the manufacturer's resistance-temperature curve; a reading of zero or infinity confirms sensor failure. They will also inspect the full wiring loom from probe to PCB for corrosion, chafing, or loose Molex connectors. If the probe and wiring are sound, they will assess the PCB input circuit for damage.
- Replace the faulty component Gas Safe engineer
Once the engineer has identified the failed part — most commonly the NTC thermistor, sometimes associated wiring — they will fit a replacement. Chaffoteaux/Ariston NTC temperature sensors (e.g. part 61000733) are widely available from trade suppliers. After replacement the engineer will clear the fault code, run the boiler through a heating and hot-water cycle, and confirm stable temperature readings before signing off the job.
Parts you may need
- NTC temperature sensor / thermistor (e.g. Ariston/Chaffoteaux part 61000733) · from £15
- Zone probe wiring loom / connector harness · from £25
- Main PCB (model-specific) · from £280
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
Can I fix a Chaffoteaux 415 fault myself?
The initial checks — a single reset, confirming gas supply, and topping up system pressure — are straightforward and safe for a homeowner. However, testing and replacing the NTC probe or inspecting the PCB requires working on the boiler's internal components, which must only be done by a Gas Safe registered engineer. Attempting this yourself is both unsafe and, for gas work, illegal in the UK.
How much does it cost to fix a Chaffoteaux 415 fault?
For the most common repair — replacing the NTC thermistor and any damaged wiring — expect to pay roughly £120–£300 all-in, covering the call-out, labour, and the part itself (sensors typically cost £10–£30 at trade). If the main PCB turns out to be the cause, costs can rise significantly, often £350–£500 or more depending on the model, so it is worth getting a firm quote before authorising PCB replacement.
Why does my boiler keep showing 415 after I reset it?
A fault that clears on reset but returns within minutes or hours almost always indicates a hardware problem — typically a failing thermistor whose resistance is drifting out of range, or an intermittent wiring short. Repeated resets will not cure the underlying fault. Book an engineer to test the probe and wiring so the root cause can be addressed properly.
Which Chaffoteaux models display fault code 415?
Code 415 appears on Chaffoteaux boilers that have a digital fault-code display, including models in the Talia, Talia Green, Pigma, Inoa, Serelia, and Mira ranges. Older Chaffoteaux boilers such as the Britony used LED flash sequences rather than numeric codes, so a three-digit display code like 415 would not appear on those models. If you are unsure of your model, check the data label on the boiler casing or inside the front panel.