Chaffoteaux 252 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 252 fault code mean?
Fault code 252 on a Chaffoteaux boiler indicates an anomaly on the domestic hot water (DHW) temperature sensor circuit. The boiler's PCB has detected either an open circuit or a short circuit on the NTC thermistor responsible for monitoring hot water temperature. When this sensor misbehaves, the PCB cannot accurately track how hot the water is, so the boiler may refuse to produce hot water, lock out, or cycle erratically. Code 252 sits within Chaffoteaux's 200-series fault group, which covers DHW circuit anomalies across modern ranges including the Inoa, Talia, Mira C Green, and Niagara. Related codes in this group include 250, 251, 253, and 254 — all pointing to variations of DHW probe or sensor faults. Always confirm the exact definition against your specific model's manual, as older LED-flash models and newer digital-display models can differ slightly in their code assignments.
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 or degraded NTC thermistor Common
The NTC thermistor is a temperature-sensitive resistor whose electrical resistance changes predictably as water temperature rises or falls. Over time, especially in older or poorly maintained systems, the sensor element can drift out of specification, fail entirely, or produce unstable readings. When this happens the PCB cannot calculate the correct water temperature, and code 252 is triggered.
- Loose, corroded, or damaged wiring Common
Even if the thermistor itself is in good condition, a loose plug, corroded terminal, or damaged section of the wiring harness between the sensor and the PCB can cause intermittent or absent signals that look identical to a failed sensor. Vibration and age are common culprits, and this is worth checking before ordering a replacement part.
- Water ingress at the sensor connection Sometimes
A nearby internal leak or a poorly sealed previous repair can allow moisture to reach the sensor connector. This can cause corrosion of the terminals, short-circuit the signal, or create erratic resistance readings that trigger the fault code.
- Scale or sludge build-up around the sensor pocket Sometimes
In hard-water areas or systems without adequate inhibitor, limescale or sludge can accumulate around the sensor pocket. This doesn't usually destroy the electrical element outright, but it can slow the sensor's thermal response, causing the PCB to receive delayed or inaccurate temperature data.
- Incorrectly seated or poorly fitted sensor Sometimes
If a sensor has been disturbed during a previous service and not refitted snugly, or if it was never seated correctly from the factory, it may not make proper thermal contact with the pipe or pocket it monitors. The resulting temperature readings will be unreliable even though the sensor tests electrically correct.
- PCB fault Rare
In a small number of cases the thermistor and its wiring both test within specification, but the PCB itself is misreading or failing to process the incoming signal correctly. A PCB fault is typically only confirmed after all other possibilities have been ruled out, as it represents the most costly repair option.
How to fix it
- Reset the boiler once DIY safe
A single reset can sometimes clear a transient electronic glitch. Press and hold the reset button as described in your boiler's user guide. If the code returns immediately or the boiler locks out again after a short run, do not continue resetting — repeated resets without resolving the underlying fault can mask the problem and may indicate something more serious.
- Check and restore system pressure if needed DIY safe
Look at the pressure gauge on the boiler's front panel. The reading should typically be between 1.0 and 1.5 bar when the system is cold. If it has dropped below 0.8 bar, top it up using the filling loop until it reads around 1.2 bar, then attempt a reset. Low pressure can sometimes contribute to temperature-related symptoms, though it is unlikely to be the sole trigger for code 252.
- Call a Gas Safe registered engineer to diagnose the fault Gas Safe engineer
All work inside the boiler casing — including inspecting the NTC sensor, its wiring harness, and connections to the PCB — must be carried out by a Gas Safe registered engineer. An engineer will review the boiler's fault history, take live temperature readings, and visually inspect the sensor plug and wiring for corrosion, moisture damage, or loose connections.
- Engineer to test sensor resistance with a multimeter Gas Safe engineer
The engineer will measure the electrical resistance of the NTC thermistor and compare it against Chaffoteaux's specification for the ambient temperature at the time of testing. At around 25°C a healthy sensor should read within the manufacturer's expected resistance range. A reading that is open-circuit, short-circuit, or significantly outside tolerance confirms the sensor has failed and needs replacing.
- Engineer to inspect for water leaks around the sensor pocket Gas Safe engineer
The engineer will check for any signs of moisture or active leaking near the sensor location. Water ingress can damage both the sensor and the connector, and any leak must be repaired before a new sensor is fitted to prevent the fault recurring.
- Engineer to replace the NTC thermistor if confirmed faulty Gas Safe engineer
A genuine Ariston/Chaffoteaux replacement NTC thermistor (such as part no. 61000733) is an inexpensive component, typically costing around £10–£35. The replacement usually involves draining a small amount of water from the relevant circuit, swapping the sensor, reconnecting the plug securely, and testing operation. The boiler should then be reset and run through a hot water draw to confirm the fault has cleared.
- Engineer to investigate PCB if sensor and wiring test correctly Gas Safe engineer
If the sensor resistance is within specification and the wiring is undamaged, the engineer will consider whether the PCB is failing to interpret the signal correctly. PCB faults typically require component-level testing or board replacement, and may warrant a cost comparison against a new boiler, particularly if the boiler is more than ten years old.
Parts you may need
- Chaffoteaux/Ariston NTC thermistor (DHW sensor, e.g. part no. 61000733) · from £15
- Wiring harness/sensor connector · from £20
- 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–£300, depending on the underlying cause.
Frequently asked questions
Can I fix Chaffoteaux fault code 252 myself?
The only DIY steps that are safe and appropriate are a single boiler reset and checking that your system pressure is within the normal 1.0–1.5 bar range. Everything else — accessing the sensor, testing wiring, or replacing any component — must be done by a Gas Safe registered engineer. Attempting to work on the boiler's internal parts yourself is unsafe and could void any remaining warranty.
How much does it cost to repair a Chaffoteaux 252 fault in the UK?
For a straightforward NTC thermistor replacement, most homeowners pay in the region of £100–£180 all-in, covering the engineer's callout, labour, and the relatively inexpensive sensor part. If the wiring harness also needs attention, costs can edge toward £200–£300. A PCB replacement — only needed in a minority of cases — can push the total to £400 or more. Always get a diagnosis before agreeing to replace expensive components.
What other fault codes are related to code 252 on a Chaffoteaux boiler?
Code 252 belongs to Chaffoteaux's 200-series DHW sensor group. Codes 250, 251, 253, and 254 all relate to variations of DHW probe or sensor anomalies on the same circuit. If you are seeing one of those codes rather than 252, the diagnostic approach is similar, but your engineer should confirm the exact definition for your specific model and age of boiler, as there are minor differences between ranges.
My Chaffoteaux boiler is over 10 years old — is it worth repairing a fault code 252?
An NTC sensor replacement is one of the less expensive boiler repairs, so it is generally worth doing even on an older boiler. However, if your engineer finds the PCB is also failing, or if other components are showing wear, it may be more cost-effective to replace the boiler altogether. Chaffoteaux boilers typically have a serviceable lifespan of around 10–15 years with regular servicing. Ask your engineer for an honest assessment of the boiler's overall condition before committing to a major repair.