Chaffoteaux 204 Fault Code: Causes, Fixes & Repair Costs
What does the Chaffoteaux 204 fault code mean?
Fault code 204 on a Chaffoteaux boiler indicates that the PCB has detected an abnormal or absent signal from the solar collector NTC (negative temperature coefficient) temperature sensor. This typically means the sensor has either developed an open circuit — where the electrical connection is broken — or a short circuit, where damaged wiring or moisture ingress causes an unintended connection. Because the boiler can no longer obtain reliable temperature data from the solar collector circuit, it locks out as a safety precaution. This is generally a non-volatile (permanent) fault, meaning a simple reset alone will not resolve it — the underlying cause must be identified and rectified before normal operation resumes.
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
- Faulty or failed solar collector NTC sensor Common
The NTC probe itself is the most frequent culprit. Over time these small sensors degrade, crack, or burn out, causing their resistance to fall outside the range the PCB expects. Once the PCB can no longer get a credible temperature reading, it raises fault code 204.
- Loose, corroded, or disconnected wiring connector Common
The wiring harness between the solar collector sensor and the PCB can work loose, corrode at the connector pins, or pull away from its socket — particularly in installations exposed to damp or temperature extremes. This mimics an open-circuit sensor fault even when the probe itself is fine.
- Damaged sensor wiring or short circuit Sometimes
If the insulation on the sensor cable has worn through, been pinched, or absorbed moisture, the wires can short together or to earth. The PCB interprets the resulting resistance reading as a faulty probe and triggers code 204.
- PCB fault Rare
In a small number of cases the printed circuit board itself is the root cause — either a failed input channel, a damaged solder joint, or general board deterioration means the PCB misreads a perfectly healthy sensor. This is worth considering only after the sensor and wiring have been confirmed to be in good order.
How to fix it
- Attempt a single boiler reset DIY safe
Press the reset button on the boiler's front panel once and wait about 60 seconds to see whether the boiler fires up normally. If it locks out again immediately, do not keep resetting — repeated resets will not clear a genuine sensor fault and could mask a more serious problem. Move on to the next step.
- Check the solar collector sensor wiring for obvious damage Gas Safe engineer
A Gas Safe engineer should inspect the wiring loom and connector between the solar collector probe and the PCB. Loose connector pins, signs of corrosion, or visible damage to the cable insulation are often all that is needed to explain the fault — and a re-seat or connector replacement is a quick, low-cost fix.
- Test the NTC sensor resistance with a multimeter Gas Safe engineer
The engineer will disconnect the sensor and measure its resistance across the specified temperature range using a multimeter. An NTC sensor should show a predictable, smoothly decreasing resistance as temperature rises. Readings that are open-loop (infinite resistance), near zero (short circuit), or erratic confirm the sensor has failed and needs replacing.
- Replace the solar collector NTC temperature probe Gas Safe engineer
If testing confirms sensor failure, the engineer will fit a replacement NTC probe compatible with your Chaffoteaux model. This is typically a straightforward parts-and-labour job and represents the most common resolution for code 204. After fitting, the fault code should clear and the boiler should resume normal operation.
- Inspect and test the PCB if the fault persists after sensor replacement Gas Safe engineer
Should fault code 204 return even with a confirmed good sensor and sound wiring, the engineer will assess the PCB. In some cases a cracked solder joint can be repaired on-site; more often a full board replacement is needed. The engineer will advise on whether repair or replacement is more cost-effective given the age of the boiler.
- Call a Gas Safe registered engineer Gas Safe engineer
All internal boiler work — including sensor testing, component replacement, and PCB inspection — must be carried out by a Gas Safe registered engineer. Do not attempt to open the boiler casing or work on any internal components yourself. You can find a local Gas Safe engineer at gassaferegister.co.uk.
Parts you may need
- Solar collector NTC temperature sensor/probe · from £25
- Sensor wiring harness or connector · from £18
- Chaffoteaux PCB (model-specific) · from £220
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–£280, depending on the underlying cause.
Frequently asked questions
Can I fix Chaffoteaux fault code 204 myself by resetting the boiler?
You can try a single reset — sometimes a transient glitch triggers the code and it clears straight away. However, code 204 is classified as a permanent (non-volatile) fault, which means the boiler will lock out again almost immediately if the solar collector sensor is genuinely faulty. If one reset does not resolve it, you will need a Gas Safe registered engineer to diagnose and replace the sensor or repair any wiring fault.
How much does it cost to fix fault code 204 on a Chaffoteaux boiler?
For the most common repair — replacing the solar collector NTC probe along with the engineer's call-out — most homeowners pay in the region of £100 to £280. If the PCB is also found to be faulty, the total cost is typically higher, often £300 to £500 depending on the model and labour rates in your area. It is worth getting two or three quotes. If your boiler is over 10–12 years old and the PCB needs replacing, it may be worth considering a new boiler instead.
What is a solar collector NTC probe and why does it matter?
An NTC (negative temperature coefficient) probe is a small electronic temperature sensor. In a Chaffoteaux boiler with solar integration, this probe monitors the temperature of the fluid returning from the solar collector panels. The PCB uses this data to coordinate between the solar circuit and the boiler's heating and hot water functions. If the sensor fails or its signal is lost, the boiler cannot safely manage that circuit and shuts down to prevent overheating or incorrect operation.
Will fault code 204 affect my central heating as well as my solar hot water?
It depends on your system setup. Because code 204 specifically relates to the solar collector sensor, the boiler will typically lock out the solar circuit rather than your entire heating system — though some Chaffoteaux models will lock out completely until the fault is cleared. Either way, get an engineer out promptly: running the system with a persistent sensor fault can place additional strain on the PCB over time.