Chaffoteaux 413 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 413 fault code mean?
Fault code 413 indicates that the boiler's external zone control board has detected a problem with the Zone 3 ambient (room) temperature sensor. This is part of a closely related family of codes: 411 signals a Zone 1 sensor issue, 412 a Zone 2 sensor issue, and 413 specifically points to Zone 3. Because these zones are managed by an external electronic board, this fault will only appear on multi-zone Chaffoteaux installations — typically where a zone controller is managing two or more separate heating circuits. The sensor in question is an NTC 10 kΩ thermistor that continuously feeds ambient temperature data back to the control board; when its resistance drifts outside the acceptable range (open circuit or short circuit), or communication on the eBus breaks down, the boiler logs fault 413 and may stop heating that zone.
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 Zone 3 NTC thermistor (room sensor) Common
The Zone 3 ambient sensor is an NTC 10 kΩ thermistor. Over time, the sensor element can degrade or fail outright, sending a resistance value that is either infinite (open circuit) or near zero (short circuit) — both of which fall outside the tolerance window the control board will accept. This is the single most common reason for a 413 fault and is typically a straightforward, low-cost fix.
- Damaged, loose, or corroded wiring Common
A break in the cable run between the Zone 3 room sensor and the external zone controller, or a loose or corroded terminal at either end, can mimic a sensor failure entirely. The sensor itself may be perfectly healthy; it is simply not making reliable electrical contact with the board.
- Moisture on the sensor or board connector Sometimes
Condensation or a minor water ingress at the sensor connector or at the corresponding terminal on the external PCB can corrupt the resistance reading. Moisture can cause intermittent faults that come and go, making diagnosis trickier than a straightforward sensor failure.
- eBus communication fault Sometimes
The external zone controller communicates with the main boiler controller via the eBus data bus. A disruption in this communication — caused by electrical interference, a wiring fault on the bus, or a partially failing component — can cause the boiler to incorrectly report a Zone 3 sensor error even when the sensor itself is undamaged.
- Faulty external zone control PCB Rare
If the external electronic board that manages the zone sensors develops a fault, it may misread or fail to read the Zone 3 sensor signal altogether. This is the least common root cause and typically only surfaces after all other possibilities have been ruled out, but it is the most expensive to resolve.
How to fix it
- Reset the boiler and observe whether the fault returns DIY safe
Press and hold the reset button as described in your boiler's user guide. A transient electrical glitch can occasionally trigger a 413 code. If the boiler resumes normal operation and the fault does not reappear within a short period, monitor it closely. If it returns, proceed with the steps below. Limit resets to two or three attempts.
- Check that the Zone 3 room sensor is correctly seated and undamaged DIY safe
Locate the Zone 3 room thermostat or sensor unit on the wall. Visually inspect it for obvious physical damage, a dislodged casing, or signs of dampness around the unit. Do not open the sensor unit or attempt any internal work — this step is purely a visual external check.
- Inspect the visible cable run from the Zone 3 sensor back to the zone controller DIY safe
Trace the wiring from the room sensor unit along the wall to where it enters the zone controller or boiler housing. Look for any obvious cable damage such as kinks, pinched sections, chafing against sharp edges, or areas where the cable may have been disturbed. Note any findings to pass on to the engineer.
- A Gas Safe engineer should test the Zone 3 sensor resistance Gas Safe engineer
Using a multimeter, an engineer will measure the resistance of the NTC thermistor across its terminals. At typical room temperature (around 20 °C), an NTC 10 kΩ sensor should read close to 10,000 ohms. A reading of zero or infinity confirms a failed sensor. Values significantly outside the expected range at the measured temperature also indicate a faulty sensor requiring replacement.
- A Gas Safe engineer should check for moisture at connectors and replace the sensor if necessary Gas Safe engineer
The engineer will inspect the sensor connector and the corresponding socket on the external PCB for any signs of moisture, oxidation, or corrosion. If moisture is present, connectors should be dried and treated appropriately. If the sensor resistance is outside specification, the NTC thermistor (Ariston/Chaffoteaux-compatible part, e.g. reference 61000733) should be replaced.
- A Gas Safe engineer should inspect the eBus wiring and connections Gas Safe engineer
If replacing the sensor does not clear the 413 fault, the engineer should test continuity and signal integrity on the eBus wiring between the external zone board and the main boiler controller. Loose or degraded bus wiring can cause the board to report spurious sensor faults.
- A Gas Safe engineer should test and, if necessary, replace the external zone control PCB Gas Safe engineer
If all wiring, connectors, and the sensor itself have been verified as healthy and the fault persists, the external electronic board is the likely culprit. The engineer should test the board's outputs before condemning it, as PCB replacement is the most costly outcome. A compatible replacement board must be fitted and commissioned by a Gas Safe registered engineer.
- Call a Gas Safe registered engineer if you have not already done so Gas Safe engineer
Beyond the initial visual checks described above, fault 413 requires diagnosis and repair by a Gas Safe registered engineer. You can find a local registered engineer at gassaferegister.co.uk. When calling, quote the fault code 413, your boiler model, and any observations you have already made about the Zone 3 sensor or wiring.
Parts you may need
- Zone 3 NTC 10 kΩ room temperature sensor (Ariston/Chaffoteaux compatible, e.g. ref. 61000733) · from £18
- External zone control PCB (Chaffoteaux multi-zone) · from £220
- eBus connecting cable / wiring harness · from £25
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
Will fault code 413 stop my boiler from working completely?
Not necessarily. Because fault 413 is specific to the Zone 3 ambient sensor on a multi-zone system, other zones may continue to function normally. The boiler may lock out heating to Zone 3 only, or it may raise a warning without a full lockout, depending on the model and how the system is configured. You should still arrange for an engineer to diagnose the fault promptly, as running a zone with an unmonitored sensor is not ideal and the fault may escalate.
Is fault code 413 related to codes 411 and 412?
Yes — codes 411, 412, and 413 are a family of related faults, all managed by the external zone control board. Code 411 indicates a fault with the Zone 1 room sensor, 412 points to Zone 2, and 413 to Zone 3. The diagnosis and repair process is essentially the same for all three; only the affected zone circuit differs. If you see 411 or 412 on your display instead, the same causes and steps apply to those respective zones.
How much does it typically cost to fix a Chaffoteaux 413 fault?
If the fault turns out to be a wiring or connector issue, most homeowners pay £80–£150 for an engineer's time to locate and repair the connection. A Zone 3 sensor replacement including parts and labour typically comes to £100–£250. The repair only becomes significantly more expensive if the external zone control PCB needs replacing, which can add £180–£400 for the part alone on top of labour, pushing total costs towards £350–£550 or more. The good news is that PCB replacement is the least common outcome — the majority of 413 faults are resolved with a new sensor or a simple wiring fix.
Can I replace the Zone 3 room sensor myself to save money?
The room sensor is a low-voltage component rather than a gas component, so it does not legally require a Gas Safe registered engineer to replace in all circumstances. However, because it is part of a multi-zone system managed by an external PCB, incorrect wiring or fitting an incompatible sensor can damage the control board or introduce further faults. Given that the sensor itself costs around £15–£25, the labour saving is modest, and most reputable heating engineers will include sensor replacement as part of their diagnostic visit. We recommend having a qualified engineer carry out the work to ensure correct testing, correct part selection, and a proper fault clearance confirmation.